You are trying to use a feature that is currently in Premium.
I guess the issue here is that the error isn’t very descriptive. It says that the project is not found which suggests an issue with the setup. If it’s not possible to move the feature to community edition it would be nice if you could at least make the error more descriptive of what the issue actually is.
You should be able to set up the CI/CD tunnel with GitLab CE. We are in the process of discussing what other features will be available in GitLab Free and what remains Premium.
That doesn’t seem to work for me with repositories other than the one with the agent config. Could you maybe take a look at the issue I have here? Kubernetes contexts from agent not injected into pipeline of projects authorized to use the agent