The endpoints https://developer.github.com/v3/apps/installations/#add-repository-to-installation and https://developer.github.com/v3/apps/installations/#remove-repository-from-installation have confusing documentation. It says that an installation token is required to access the endpoints but in this forum I’ve read that that’s not possible. My experience appears to confirm this.
I tried to use the endpoints with basically all kinds of tokens - unsuccessfully. Is it that these endpoints can not be used with any OAuth token? If it is possible, what are the pre conditions? I tried them on a repository on my own account on which I also have the installation. I tried it with the normal OAuth token and the GitHub App OAuth token as well as the installation token.