We don’t support deploying from private registries yet. We will at some point, but no timeframe. Until then it’s common to pull from the private registry then push to your fly repo from an authenticated docker client. Are you trying to do that from a machine without a docker client installed? You can SSH into the builder app — changes are persisted in the volume, but credentials come from the client so it might not help with what you need.
You’ve found a number of sharp corners we didn’t know existed. I really appreciate your patience while we get them fixed!