When a project requires that all discussions are resolved for an MR to be merged, and you try to merge an MR in the API where there are unresolved discussions, you are presented with a simple "405 Method Not Allowed.". This can make it hard to figure out why a merge failed. The problem in the API code appears to be the following: ```ruby not_allowed! unless merge_request.mergeable_state?(skip_ci_check: merge_when_pipeline_succeeds) ``` This leads to the following code: ```ruby def mergeable_state?(skip_ci_check: false, skip_discussions_check: false) return false unless open? return false if work_in_progress? return false if broken? return false unless skip_ci_check || mergeable_ci_state? return false unless skip_discussions_check || mergeable_discussions_state? true end ``` This leads to: ```ruby def mergeable_discussions_state? return true unless project.only_allow_merge_if_all_discussions_are_resolved? !discussions_to_be_resolved? end ``` It would be nice if the error included a short message that describes _why_ the merge failed.