GitHub Actions submodule checkout failed on a private submodule

GitHub Actions submodule checkout failed is a credential message rather than a git one: the outer repository clones cleanly and only the submodule fetch stops. The credential the action configured is scoped to the repository running the workflow, and a submodule usually lives somewhere else. Two independent decisions: what the .gitmodules URL looks like, and whether checkout was allowed to persist a credential at all. What this error means The checkout step is green for several seconds, prints the submodule update command, starts cloning the first submodule and then stops. Git asks for a username, finds it cannot prompt because the runner has no terminal, and gives up. The outer repository is fully checked out on disk, which is what makes this read like a corrupt submodule pointer rather than a permissions problem. Remove submodules from the step and everything is green again, which is the strongest hint that nothing about the repository itself is wrong. ```Quoted from a