200 – OK ： This means that the GET , PUT, or DELETE request was successful. When you request a resource, it will be returned in JSON format.
201 – Created : This means that the POST request was successful. This status code is only returned when you try to create a new resource. The resource will also be returned to you.
400 – Bad Request : This mean you have missed a required attribute for this request. For example, the title for a merge request was not given.
401 – Unauthorized ： This means that you are not authenticated. If you don’t send a secret token with your request or send an invalid token, this status is returned.
403 – Forbidden : This means that you are authenticated but don’t have the required permissions to perform thte given request. This can happen, for example , if you try to delete a project but you’re not an owner of the project.
404 – Not Found : This means that the resource you’re trying to fetch dose not exist. For example, you try to request an issue by its ID, but that issue could not be found.
405 – Method not allowed ： This means that GitLab does not support the request you try to perform.
409 – Conflict : This means that a conflicting resource alreadly exists; for example , you try to create a project with the same name as a project that was already created.
500 – Server error : This means that something went wrong with your request. This was a server-side issue, so you don’t have to alter your message. You might find a bug in Gitlab.