A 400 error returns for web services data action integrations in the following scenarios:

• When you create a custom action with a non-JSON type Accept header, the create action fails.

  {
      "status": 400,
      "errorCode": "INVALID_SCHEMA",
      "userMessage": "The 'Accept' header only supports json content types when specified",
      "userParams": [],
      "correlationId": "7930ce0c-ec9e-4929-9a70-0fe087b518b2",
      "details": [
          {
              "errorCode": "ACTION.PROCESSING"
          }
      ],
      "errors": []
  }

  When you configure the custom action, ensure that you set the Accept header value to a JSON media type. For example, application/json.

• A custom action execution returns a non-JSON response.

  {
  
      "status": 400,
      "errorCode": "BAD_REQUEST",
      "userMessage": "The request could not be understood by the server due to malformed syntax.",
      "userParams": [ ],
      "correlationId": "fbb8bb72-0637-4028-b7d8-caba6686244b",
      "details": [
          {
              "errorCode": "ACTION.REMOTE_ENDPOINT"
          }
      ],
      "errors": [
          {
              "status": 400,
              "errorCode": "BAD_REQUEST",
              "userMessage": "REST call for action execute failed. Message: Request to backend service failed. To see error details, use test mode to execute the action, or execute request in Postman or other REST tools. [fbb8bb72-0637-4028-b7d8-caba6686244b]",
              "userParams": [],
              "details": [],
              "errors": []
          }
      ]
  }

  This error mostly occurs when a non-JSON response body from the action’s endpoint cannot be parsed.

For more information about the integration, see About the web services data actions integration, Test data actions, and Add configuration to custom actions.