Redmine

I see I actually tested this with older version before - 2.6.0, not 2.6.2. So I missed that change in 2.6.1.
Maybe this REST operation should be idempotent ?

Alex Last wrote:

I see I actually tested this with older version before - 2.6.0, not 2.6.2. So I missed that change in 2.6.1.

That was not really a change but a fix, this would trigger a 500 error before 2.6.1

Maybe this REST operation should be idempotent ?

POST requests are generally not. The few examples of REST API I was able to find respond with a 409 in this case, maybe we can change it to 409 instead of 422 for when the user already belongs to the group. Also, a 404 should be sent instead of a 422 for when the user does not exist. What do you think?

I don't have a strong preference on 409 vs. 200 response code. but I don't see a harm in making this operation idempotent, so 200 would be more appropriate.
404 error code for non-existing user seems right as long as it is clear in the response what exactly is not found - user or group.