Here are listed all of the possible response codes of API requests.
| Parameter | Value |
| 101 | OK Request was successful. |
| 201 | Data must be posted with POST method Wrong request method used. POST method is required. |
| 203 | Invalid data submitted - ... Parameter validation error. Check to make sure all parameters have a proper value. |
| 204 | Invalid email address provided - … Email address syntax error. |
| 206 | Could not find requested email address Subscriber with requested email address does not exist in the database. |
| 207 | Following fields are required - ... Request is missing one (or several) required fields. |
| 208 | Could not find list with ID - … Segment with requested ID does not exist. |
| 209 | Could not load content from remote URL - … Unable to fetch template HTML from remote URL. Please make sure the URL is publicly available and returns HTTP 200 OK. |
| 210 | Invalid due date provided Due date field is empty or not in the required format. |
| 211 | Domain of From address is unverified Domain of the provided From address is not verified. Learn more from domain verification user guide. |
| 212 | Launch failed with error - … Error when launching a campaign or A/B test. |
| 213 | Invalid win date provided A/B test winning section due date is empty, in wrong format or before due date. |
| 214 | Invalid winning condition provided Winning condition isn’t one of the possible options as specified in the documentation. |
| 215 | Invalid campaign ID provided Provided campaign ID is empty or in the wrong format. |
| 216 | Could not find campaign matching provided ID Campaign with provided ID does not exist. |
| 217 | Unknown column in filter data - … Field in the segmentation rule does not exist. |
| 218 | Unknown operator … for field … Unsupported segmentation operator. |
| 219 | Could not find list with ID - ... Segment with provided ID does not exist. |
| 220 | Could not find statistics entry by email - ... Cannot find statistics entry by email address. It could also mean that the statistics entry has not been written to the database, yet. |
| 221 | Invalid autoresponder ID provided Automation workflow with specified ID does not exist, workflow is disabled, organization does not have enough credit to queue messages, or workflow has wrong trigger. |
| 223 | Missing start or end date Subscriber action log request start or end date parameter is empty or missing. |
| 224 | End date cannot be before start Subscriber action log request start date is more than end date value. |
| 225 | Database insert failed Internal server error while communicating with database server. |
| 226 | Failed to download file from URL - … Unable to fetch attachment from remote URL. Please make sure the URL is publicly available and returns HTTP 200 OK. |