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Last tested: Jul 24, 2020
We saw one case where a user was seeing this error, despite setting up the deploy key correcting in Gitlab.
In this case, the user was able to resolve this by creating a README.md file in the repo. Since the repo was completely empty, no branches, they couldn't make the connection. Adding the README.md let them verify the write access. This may have had to do with the fact that the user was using a protected master branch, though we could not recreate the behavior.