Error during tag/untag user

Been dealing with this pretty annoying issue that makes no sense:

The solution? Change tag_users controller from this:

json_response(conn, :no_content, "")

to this:

json_response(conn, 200, "")

wtf?

Btw the tag/untag action happens successfully, it's just the server returns an error afterwards. I tried setting it to 204 and that also breaks it, it's gotta be 200.