Deployment issue -- "remote builder app unavailable"

Okay, it got further. But Now I get this on deploy. (This is a freshly generated Phoenix app, per your documentation.)

==> Creating release
Release v2 created
Release command detected: this new release will not be available until the command succeeds.

You can detach the terminal anytime without stopping the deployment
==> Release command
Command: /app/bin/migrate
	 Starting instance
	 Configuring virtual machine
	 Pulling container image
	 Unpacking image
	 Preparing kernel init
	 Configuring firecracker
	 Starting virtual machine
	 Starting init (commit: aa54f7d)...
	 Preparing to run: `/app/bin/migrate` as nobody
	 2022/05/16 17:56:03 listening on [fdaa:0:5c43:a7b:88dc:1e7d:40b0:2]:22 (DNS: [fdaa::3]:53)
	 Main child exited normally with code: 0
	 Reaped child process with pid: 566 and signal: SIGUSR1, core dumped? false
	 Starting clean up.
Error Release command failed, deployment aborted