diff --git a/services/nginx/app/modules/economic/economic_m.php b/services/nginx/app/modules/economic/economic_m.php
index 5a8594c7..4ca13c8e 100644
--- a/services/nginx/app/modules/economic/economic_m.php
+++ b/services/nginx/app/modules/economic/economic_m.php
@@ -155,14 +155,15 @@ class economic_m
         $details = [];
 
         if (isset($decoded['errors']) && is_array($decoded['errors'])) {
-            $safeErrors = [];
-            foreach ( $decoded['errors'] as $error ) {
-                if (is_scalar($error)) {
-                    $safeErrors[] = (string)$error;
-                }
+            $flattenedErrors = array_values(array_unique($this->flatten_economic_errors($decoded['errors'], 'errors')));
+            if (!empty($flattenedErrors)) {
+                $details['errors'] = $flattenedErrors;
             }
-            if (!empty($safeErrors)) {
-                $details['errors'] = $safeErrors;
+        }
+        if (isset($decoded['developerHint']) && is_string($decoded['developerHint'])) {
+            $developerHint = trim($decoded['developerHint']);
+            if ($developerHint !== '') {
+                $details['developerHint'] = $developerHint;
             }
         }
 
@@ -184,4 +185,45 @@ class economic_m
             . ' | details='
             . json_encode($details, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES);
     }
+
+    /**
+     * @return string[]
+     */
+    protected function flatten_economic_errors(mixed $value, string $path = ''): array
+    {
+        if (is_string($value)) {
+            $message = trim($value);
+            if ($message === '') {
+                return [];
+            }
+            return [$path !== '' ? ($path . ': ' . $message) : $message];
+        }
+
+        if (!is_array($value)) {
+            return [];
+        }
+
+        $messages = [];
+        if (isset($value['errorMessage']) && is_string($value['errorMessage'])) {
+            $errorMessage = trim($value['errorMessage']);
+            if ($errorMessage !== '') {
+                $messages[] = $path !== '' ? ($path . ': ' . $errorMessage) : $errorMessage;
+            }
+        }
+
+        foreach ($value as $key => $child) {
+            if ($key === 'errorMessage') {
+                continue;
+            }
+            $segment = is_int($key) ? ('[' . $key . ']') : (string)$key;
+            $childPath = $path === ''
+                ? $segment
+                : (is_int($key) ? ($path . $segment) : ($path . '.' . $segment));
+            foreach ($this->flatten_economic_errors($child, $childPath) as $childMessage) {
+                $messages[] = $childMessage;
+            }
+        }
+
+        return $messages;
+    }
 }
diff --git a/services/nginx/app/modules/economic/endpoints/invoices/economic_invoices_drafts_endpoint.php b/services/nginx/app/modules/economic/endpoints/invoices/economic_invoices_drafts_endpoint.php
index 8582cf1c..3467e0c6 100644
--- a/services/nginx/app/modules/economic/endpoints/invoices/economic_invoices_drafts_endpoint.php
+++ b/services/nginx/app/modules/economic/endpoints/invoices/economic_invoices_drafts_endpoint.php
@@ -147,27 +147,21 @@ class economic_invoices_drafts_endpoint
         if ($public_entry_number !== null) {
             $recipient['publicEntryNumber'] = $public_entry_number;
         }
-        $attention_customer_contact_number = $customer->getAttentionCustomerContactNumber();
-        if ($attention_customer_contact_number !== null) {
-            $recipient['attention'] = [
-                'customerContactNumber' => $attention_customer_contact_number,
-            ];
+        $attention_reference = $customer->getAttentionReference();
+        if ($attention_reference !== null) {
+            $recipient['attention'] = $attention_reference;
         }
 
         $references = [
             'other' => $external_id
         ];
-        $reference_customer_contact_number = $customer->getReferenceCustomerContactNumber();
-        if ($reference_customer_contact_number !== null) {
-            $references['customerContact'] = [
-                'customerContactNumber' => $reference_customer_contact_number,
-            ];
+        $customer_contact_reference = $customer->getReferenceCustomerContact();
+        if ($customer_contact_reference !== null) {
+            $references['customerContact'] = $customer_contact_reference;
         }
-        $sales_person_employee_number = $customer->getSalesPersonEmployeeNumber();
-        if ($sales_person_employee_number !== null) {
-            $references['salesPerson'] = [
-                'employeeNumber' => $sales_person_employee_number,
-            ];
+        $sales_person_reference = $customer->getSalesPersonReference();
+        if ($sales_person_reference !== null) {
+            $references['salesPerson'] = $sales_person_reference;
         }
 
         $payload = [
@@ -204,11 +198,9 @@ class economic_invoices_drafts_endpoint
             'recipient' => $recipient,
         ];
 
-        $default_delivery_location_number = $customer->getDefaultDeliveryLocationNumber();
-        if ($default_delivery_location_number !== null) {
-            $payload['deliveryLocation'] = [
-                'deliveryLocationNumber' => $default_delivery_location_number,
-            ];
+        $default_delivery_location_reference = $customer->getDefaultDeliveryLocationReference();
+        if ($default_delivery_location_reference !== null) {
+            $payload['deliveryLocation'] = $default_delivery_location_reference;
         }
 
         // Send the request
diff --git a/services/nginx/app/modules/economic/helpers/economic_customer.php b/services/nginx/app/modules/economic/helpers/economic_customer.php
index 2f8b5fb5..a5c2d4bc 100644
--- a/services/nginx/app/modules/economic/helpers/economic_customer.php
+++ b/services/nginx/app/modules/economic/helpers/economic_customer.php
@@ -164,31 +164,61 @@ class economic_customer
     public function getAttentionCustomerContactNumber(): ?int
     {
         self::requireSelected();
-        return $this->nestedPositiveIntField(['attention', 'customerContactNumber']);
+        return $this->getAttentionReference()['customerContactNumber'] ?? null;
     }
 
     public function getReferenceCustomerContactNumber(): ?int
     {
         self::requireSelected();
-        return $this->nestedPositiveIntField(['customerContact', 'customerContactNumber']);
+        return $this->getReferenceCustomerContact()['customerContactNumber'] ?? null;
     }
 
     public function getSalesPersonEmployeeNumber(): ?int
     {
         self::requireSelected();
-        return $this->nestedPositiveIntField(['salesPerson', 'employeeNumber']);
+        return $this->getSalesPersonReference()['employeeNumber'] ?? null;
     }
 
     public function getVendorReferenceEmployeeNumber(): ?int
     {
         self::requireSelected();
-        return $this->nestedPositiveIntField(['vendorReference', 'employeeNumber']);
+        return $this->getVendorReferenceReference()['employeeNumber'] ?? null;
     }
 
     public function getDefaultDeliveryLocationNumber(): ?int
     {
         self::requireSelected();
-        return $this->nestedPositiveIntField(['defaultDeliveryLocation', 'deliveryLocationNumber']);
+        return $this->getDefaultDeliveryLocationReference()['deliveryLocationNumber'] ?? null;
+    }
+
+    public function getAttentionReference(): ?array
+    {
+        self::requireSelected();
+        return $this->nestedReferenceField(['attention'], 'customerContactNumber');
+    }
+
+    public function getReferenceCustomerContact(): ?array
+    {
+        self::requireSelected();
+        return $this->nestedReferenceField(['customerContact'], 'customerContactNumber');
+    }
+
+    public function getSalesPersonReference(): ?array
+    {
+        self::requireSelected();
+        return $this->nestedReferenceField(['salesPerson'], 'employeeNumber');
+    }
+
+    public function getVendorReferenceReference(): ?array
+    {
+        self::requireSelected();
+        return $this->nestedReferenceField(['vendorReference'], 'employeeNumber');
+    }
+
+    public function getDefaultDeliveryLocationReference(): ?array
+    {
+        self::requireSelected();
+        return $this->nestedReferenceField(['defaultDeliveryLocation'], 'deliveryLocationNumber');
     }
 
     protected function nullableStringField(string $field): ?string
@@ -206,6 +236,51 @@ class economic_customer
      * @param string[] $segments
      */
     protected function nestedPositiveIntField(array $segments): ?int
+    {
+        $value = $this->nestedObjectField($segments);
+
+        if (!is_int($value) && !is_float($value) && !is_string($value)) {
+            return null;
+        }
+
+        $number = (int)$value;
+        return $number > 0 ? $number : null;
+    }
+
+    /**
+     * @param string[] $segments
+     */
+    protected function nestedReferenceField(array $segments, string $idField): ?array
+    {
+        $source = $this->nestedObjectField($segments);
+        if (!is_object($source)) {
+            return null;
+        }
+
+        $idValue = $source->{$idField} ?? null;
+        if (!is_int($idValue) && !is_float($idValue) && !is_string($idValue)) {
+            return null;
+        }
+        $id = (int)$idValue;
+        if ($id <= 0) {
+            return null;
+        }
+
+        $reference = [
+            $idField => $id,
+        ];
+        $self = $source->self ?? null;
+        if (is_string($self) && trim($self) !== '') {
+            $reference['self'] = trim($self);
+        }
+
+        return $reference;
+    }
+
+    /**
+     * @param string[] $segments
+     */
+    protected function nestedObjectField(array $segments): mixed
     {
         $value = $this->customer_data_object;
         foreach ($segments as $segment) {
@@ -215,12 +290,7 @@ class economic_customer
             $value = $value->{$segment};
         }
 
-        if (!is_int($value) && !is_float($value) && !is_string($value)) {
-            return null;
-        }
-
-        $number = (int)$value;
-        return $number > 0 ? $number : null;
+        return $value;
     }
 
     /**
diff --git a/services/nginx/app/modules/economic/invoices/draft/economic_invoice_draft_mo.php b/services/nginx/app/modules/economic/invoices/draft/economic_invoice_draft_mo.php
index dabd833d..7a42e6fb 100644
--- a/services/nginx/app/modules/economic/invoices/draft/economic_invoice_draft_mo.php
+++ b/services/nginx/app/modules/economic/invoices/draft/economic_invoice_draft_mo.php
@@ -63,31 +63,23 @@ class economic_invoice_draft_mo extends economicInvoicesDrafts
         if ($public_entry_number !== null) {
             $recipient['publicEntryNumber'] = $public_entry_number;
         }
-        $attention_customer_contact_number = $customer->getAttentionCustomerContactNumber();
-        if ($attention_customer_contact_number !== null) {
-            $recipient['attention'] = [
-                'customerContactNumber' => $attention_customer_contact_number,
-            ];
+        $attention_reference = $customer->getAttentionReference();
+        if ($attention_reference !== null) {
+            $recipient['attention'] = $attention_reference;
         }
 
         $references = [];
-        $reference_customer_contact_number = $customer->getReferenceCustomerContactNumber();
-        if ($reference_customer_contact_number !== null) {
-            $references['customerContact'] = [
-                'customerContactNumber' => $reference_customer_contact_number,
-            ];
+        $customer_contact_reference = $customer->getReferenceCustomerContact();
+        if ($customer_contact_reference !== null) {
+            $references['customerContact'] = $customer_contact_reference;
         }
-        $sales_person_employee_number = $customer->getSalesPersonEmployeeNumber();
-        if ($sales_person_employee_number !== null) {
-            $references['salesPerson'] = [
-                'employeeNumber' => $sales_person_employee_number,
-            ];
+        $sales_person_reference = $customer->getSalesPersonReference();
+        if ($sales_person_reference !== null) {
+            $references['salesPerson'] = $sales_person_reference;
         }
-        $vendor_reference_employee_number = $customer->getVendorReferenceEmployeeNumber();
-        if ($vendor_reference_employee_number !== null) {
-            $references['vendorReference'] = [
-                'employeeNumber' => $vendor_reference_employee_number,
-            ];
+        $vendor_reference = $customer->getVendorReferenceReference();
+        if ($vendor_reference !== null) {
+            $references['vendorReference'] = $vendor_reference;
         }
 
         $data = [
@@ -112,11 +104,9 @@ class economic_invoice_draft_mo extends economicInvoicesDrafts
             $data['references'] = $references;
         }
 
-        $default_delivery_location_number = $customer->getDefaultDeliveryLocationNumber();
-        if ($default_delivery_location_number !== null) {
-            $data['deliveryLocation'] = [
-                'deliveryLocationNumber' => $default_delivery_location_number,
-            ];
+        $default_delivery_location_reference = $customer->getDefaultDeliveryLocationReference();
+        if ($default_delivery_location_reference !== null) {
+            $data['deliveryLocation'] = $default_delivery_location_reference;
         }
 
         return $this->createInvoiceDraft($data);
diff --git a/services/nginx/app/tests/Unit/Invoicing/EconomicCustomerEanHelperTest.php b/services/nginx/app/tests/Unit/Invoicing/EconomicCustomerEanHelperTest.php
index 32fcb8d4..62449186 100644
--- a/services/nginx/app/tests/Unit/Invoicing/EconomicCustomerEanHelperTest.php
+++ b/services/nginx/app/tests/Unit/Invoicing/EconomicCustomerEanHelperTest.php
@@ -23,23 +23,48 @@ it('exposes optional EAN and public entry number from fetched e-conomic customer
         'publicEntryNumber' => ' DK123456789 ',
         'attention' => (object)[
             'customerContactNumber' => 9,
+            'self' => 'https://restapi.e-conomic.com/customers/42331123/contacts/9',
         ],
         'customerContact' => (object)[
             'customerContactNumber' => 10,
+            'self' => 'https://restapi.e-conomic.com/customers/42331123/contacts/10',
         ],
         'salesPerson' => (object)[
             'employeeNumber' => 12,
+            'self' => 'https://restapi.e-conomic.com/employees/12',
         ],
         'vendorReference' => (object)[
             'employeeNumber' => 14,
+            'self' => 'https://restapi.e-conomic.com/employees/14',
         ],
         'defaultDeliveryLocation' => (object)[
             'deliveryLocationNumber' => 7,
+            'self' => 'https://restapi.e-conomic.com/customers/42331123/delivery-locations/7',
         ],
     ]);
 
     expect($customer->getEan())->toBe('5790001234567');
     expect($customer->getPublicEntryNumber())->toBe('DK123456789');
+    expect($customer->getAttentionReference())->toBe([
+        'customerContactNumber' => 9,
+        'self' => 'https://restapi.e-conomic.com/customers/42331123/contacts/9',
+    ]);
+    expect($customer->getReferenceCustomerContact())->toBe([
+        'customerContactNumber' => 10,
+        'self' => 'https://restapi.e-conomic.com/customers/42331123/contacts/10',
+    ]);
+    expect($customer->getSalesPersonReference())->toBe([
+        'employeeNumber' => 12,
+        'self' => 'https://restapi.e-conomic.com/employees/12',
+    ]);
+    expect($customer->getVendorReferenceReference())->toBe([
+        'employeeNumber' => 14,
+        'self' => 'https://restapi.e-conomic.com/employees/14',
+    ]);
+    expect($customer->getDefaultDeliveryLocationReference())->toBe([
+        'deliveryLocationNumber' => 7,
+        'self' => 'https://restapi.e-conomic.com/customers/42331123/delivery-locations/7',
+    ]);
     expect($customer->getAttentionCustomerContactNumber())->toBe(9);
     expect($customer->getReferenceCustomerContactNumber())->toBe(10);
     expect($customer->getSalesPersonEmployeeNumber())->toBe(12);
@@ -56,6 +81,11 @@ it('returns null for blank optional e-conomic customer recipient identifiers', f
 
     expect($customer->getEan())->toBeNull();
     expect($customer->getPublicEntryNumber())->toBeNull();
+    expect($customer->getAttentionReference())->toBeNull();
+    expect($customer->getReferenceCustomerContact())->toBeNull();
+    expect($customer->getSalesPersonReference())->toBeNull();
+    expect($customer->getVendorReferenceReference())->toBeNull();
+    expect($customer->getDefaultDeliveryLocationReference())->toBeNull();
     expect($customer->getAttentionCustomerContactNumber())->toBeNull();
     expect($customer->getReferenceCustomerContactNumber())->toBeNull();
     expect($customer->getSalesPersonEmployeeNumber())->toBeNull();
diff --git a/services/nginx/app/tests/Unit/Invoicing/EconomicInvoiceDraftRecipientEanWiringTest.php b/services/nginx/app/tests/Unit/Invoicing/EconomicInvoiceDraftRecipientEanWiringTest.php
index 5378591e..2bdeaefb 100644
--- a/services/nginx/app/tests/Unit/Invoicing/EconomicInvoiceDraftRecipientEanWiringTest.php
+++ b/services/nginx/app/tests/Unit/Invoicing/EconomicInvoiceDraftRecipientEanWiringTest.php
@@ -9,13 +9,13 @@ it('wires EAN and public entry number into e-conomic invoice draft recipients',
     expect($content)->toContain("\$recipient['nemHandelType'] = 'ean';");
     expect($content)->toContain('$customer->getPublicEntryNumber()');
     expect($content)->toContain("\$recipient['publicEntryNumber']");
-    expect($content)->toContain('$customer->getAttentionCustomerContactNumber()');
+    expect($content)->toContain('$customer->getAttentionReference()');
     expect($content)->toContain("\$recipient['attention']");
-    expect($content)->toContain('$customer->getReferenceCustomerContactNumber()');
+    expect($content)->toContain('$customer->getReferenceCustomerContact()');
     expect($content)->toContain("\$references['customerContact']");
-    expect($content)->toContain('$customer->getSalesPersonEmployeeNumber()');
+    expect($content)->toContain('$customer->getSalesPersonReference()');
     expect($content)->toContain("\$references['salesPerson']");
-    expect($content)->toContain('$customer->getDefaultDeliveryLocationNumber()');
+    expect($content)->toContain('$customer->getDefaultDeliveryLocationReference()');
     expect($content)->toContain("\$payload['deliveryLocation']");
     expect($content)->toContain("'recipient' => \$recipient");
 });
diff --git a/services/nginx/app/tests/Unit/Invoicing/EconomicLegacyDraftPayloadWiringTest.php b/services/nginx/app/tests/Unit/Invoicing/EconomicLegacyDraftPayloadWiringTest.php
index 10e06dd2..9c283363 100644
--- a/services/nginx/app/tests/Unit/Invoicing/EconomicLegacyDraftPayloadWiringTest.php
+++ b/services/nginx/app/tests/Unit/Invoicing/EconomicLegacyDraftPayloadWiringTest.php
@@ -9,10 +9,15 @@ it('wires legacy draft creation payload with customer e-conomic metadata and EAN
     expect($content)
         ->toContain('$customer = $this->economic->getCustomer((int)$this->customer_number);')
         ->toContain("\$recipient['nemHandelType'] = 'ean';")
+        ->toContain('$customer->getAttentionReference()')
         ->toContain("\$recipient['attention']")
+        ->toContain('$customer->getReferenceCustomerContact()')
         ->toContain("\$references['customerContact']")
+        ->toContain('$customer->getSalesPersonReference()')
         ->toContain("\$references['salesPerson']")
+        ->toContain('$customer->getVendorReferenceReference()')
         ->toContain("\$references['vendorReference']")
+        ->toContain('$customer->getDefaultDeliveryLocationReference()')
         ->toContain("\$data['deliveryLocation']")
         ->toContain("'paymentTermsNumber' => (int)\$customer->getPaymentTermsNumber()")
         ->toContain("'vatZoneNumber' => (int)\$customer->getVatZoneNumber()")
diff --git a/services/nginx/app/tests/Unit/Invoicing/EconomicUpstreamErrorFormattingTest.php b/services/nginx/app/tests/Unit/Invoicing/EconomicUpstreamErrorFormattingTest.php
new file mode 100644
index 00000000..e7afd683
--- /dev/null
+++ b/services/nginx/app/tests/Unit/Invoicing/EconomicUpstreamErrorFormattingTest.php
@@ -0,0 +1,46 @@
+<?php
+
+app_require('modules/economic/economic_m.php');
+
+it('includes nested annotated e-conomic validation errors and developer hint in runtime exceptions', function (): void {
+    $economic = new class extends economic_m {
+        public function __construct()
+        {
+            // Intentionally skip parent constructor to avoid credential requirements in tests.
+        }
+
+        public function formatForTest(int $httpStatusCode, string $response): string
+        {
+            return $this->format_upstream_error_message($httpStatusCode, $response);
+        }
+    };
+
+    $response = json_encode([
+        'message' => 'Validation failed. 2 errors found.',
+        'developerHint' => 'Review annotated errors for payload details.',
+        'errors' => [
+            'recipient' => [
+                'attention' => [
+                    'errorMessage' => 'Customer contact not found for recipient attention.',
+                ],
+            ],
+            'references' => [
+                'customerContact' => [
+                    'errorMessage' => 'Customer contact reference is invalid.',
+                ],
+            ],
+        ],
+        'logId' => 'abc123',
+        'httpStatusCode' => 400,
+    ], JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES);
+
+    expect($response)->not->toBeFalse();
+    $formatted = $economic->formatForTest(400, (string)$response);
+
+    expect($formatted)
+        ->toContain('Validation failed. 2 errors found.')
+        ->toContain('errors.recipient.attention: Customer contact not found for recipient attention.')
+        ->toContain('errors.references.customerContact: Customer contact reference is invalid.')
+        ->toContain('developerHint')
+        ->toContain('abc123');
+});