I am running fastlane match (git) on Circle CI and requires read on an extra certificates repo.
What I did:
I added a Checkout SSH key with a machine user as outline in the documentations but had access error to my repo. The machine user had the correct repo access (later I tried giving it admin access). The access error persisted. I followed the steps in https://circleci.com/docs/2.0/gh-bb-integration/#creating-a-machine-user
After looking at multiple discussions, nothing seemed to worked, most of the post just refers back to the documentation https://circleci.com/docs/2.0/gh-bb-integration/