diff --git a/src/openapi/fiko/fiko-crud.yaml b/src/openapi/fiko/fiko-crud.yaml
index 46a74ce..1c7b409 100644
--- a/src/openapi/fiko/fiko-crud.yaml
+++ b/src/openapi/fiko/fiko-crud.yaml
@@ -45,6 +45,12 @@ paths:
             application/json:
               schema:
                 $ref: "#/components/schemas/TransactionItemsBulkPostResponseBody"
+        "400":
+          description: Bad request
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/TransactionItemsBulkBadRequestResponseBody"
   /transactionitems:
     get:
       summary: Find transaction items.
@@ -1591,16 +1597,68 @@ components:
               - type
               - productCode
     TransactionItemsBulkPostResponseBody:
-      type: array
-      items:
-        type: object
-        properties:
-          transactionItemId:
-            type: string
-            format: uuid
-            example: afce35b2-1dff-4ace-98d0-4b9ac405c87d
-        required:
-          - transactionItemId
+      type: object
+      properties:
+        summary:
+          type: object
+          properties:
+            created:
+              type: integer
+              example: 15
+            updated:
+              type: integer
+              example: 2
+            total:
+              type: integer
+              example: 17
+          required:
+            - created
+            - updated
+            - total
+      required:
+        - summary
+    TransactionItemsBulkBadRequestResponseBody:
+      type: object
+      properties:
+        type:
+          type: string
+          format: url
+          example: https://htm.nl/api/v1/probs/fiko/validationerror
+        title:
+          type: string
+          example: Transaction validation failed.
+        detail:
+          type: string
+          example: One ore more transactions in the request are invalid.
+        instance:
+          type: string
+          example: urn:uuid:4017fabc-1b28-11e8-accf-0ed5f89f718b
+        errors:
+          type: array
+          items:
+            type: object
+            properties:
+              detail:
+                type: string
+                example: Transaction is a duplicate of a transaction already in the system.
+              pointer: 
+                type: string
+                example: "#/transactionItems/0"
+              transactionId:
+                type: string
+                example: 1ad109d3-fd7d-4b6f-872b-220d492f385f
+              transactionLineId:
+                type: string
+                example: fee907dd-e59d-44f5-a63b-bbdec38f79b7
+            required:
+              - detail
+              - pointer
+              - transactionId
+      required:
+        - type
+        - title
+        - detail
+        - instance
     TransactionItemsPatchRequestBody:
       type: object
       properties:
@@ -2529,7 +2587,7 @@ components:
         taxCode:
           type: string
           example: V21
-        taxPercentageAmount:  
+        taxPercentageAmount:
           type: integer
           example: 21
         description:
@@ -2559,7 +2617,7 @@ components:
         sourceMetadata:
           type: array
           items:
-            $ref: '#/components/schemas/SourceMetadata'
+            $ref: "#/components/schemas/SourceMetadata"
         href:
           type: string
           nullable: true
@@ -2731,7 +2789,7 @@ components:
                 format: uuid
                 example: e0af8c8f-d421-4567-a14e-48e2a1bb86fb
               concession:
-                $ref: '#/components/schemas/Concession'
+                $ref: "#/components/schemas/Concession"
               percentage:
                 type: number
                 example: 84.021
@@ -2818,7 +2876,7 @@ components:
         concessions:
           type: array
           items:
-            $ref: '#/components/schemas/Concession'
+            $ref: "#/components/schemas/Concession"
         href:
           type: string
           nullable: true
@@ -2830,7 +2888,7 @@ components:
         failureReasons:
           type: array
           items:
-            $ref: '#/components/schemas/FailureReason'
+            $ref: "#/components/schemas/FailureReason"
         href:
           type: string
           nullable: true