Merge fails: "...requires both write access on the origin and read access on the fork."

[Christopher Lovejoy]

I've created a branch off my main branch, pushed one commit, and made a pull request from that branch back to my main branch. Upon clicking the "Merge" button in the "Merge pull request" modal window, this message appears at the bottom of the modal:

> newstatus: Fulfilling a pull request requires both write access on the origin and read access on the fork.

I'm unable to merge into my main branch, and searching this error message yields no results. Any help would be appreciated.

[Christopher Lovejoy]

Nevermind. The error message is descriptive enough: the user  permissions on the main branch had been changed without my knowledge, and I'd not yet found the branch user permissions editor in settings.