May be the free Fly builder is gone. Either you can try to recreate the builder, or deploy with fly deploy --local-only <other-args> to see if it then recovers your app.
This is worrying, because ideally, Fly should have restarted the VM unless something scaled it down to zero, or got rid of it. If you’re on the launch plan, you should email support email specific to your org: I can’t deploy the application!!! - #3 by undefined