Before contacting support, re-read the descriptions of the inputs in the Options sections of README.md and double check that you have specified the corret project_id, auth_project_number, service_account, etc.
If the problem still persists, something might be wrong with the Connect Gateway, which might cause trouble for logging in. Please contact the SKIP team if this is the case.
If you experience having a locked terraform workload, run terraform force-unlock by providing the LOCK_ID as the unlock input in run-terraform.
You can set the destroy input in run-terraform to true in order to run terraform destroy where the apply step usually is. This will destroy all the infrastructure in your working folder, so do not use this without understanding the implications.