flyctl deploy fails on "Create release", results in an error connecting to the Fly API

More details about what I am doing wrong would be appreciated in the error message.

$ flyctl deploy
==> Verifying app config                                                                                                                                                                      
--> Verified app config                                                                                                                                                                       
==> Building image                                                                                                                                                                            
Searching for image 'mumblevoip/mumble-server' remotely...                                                                                                                                    
image found: img_lrjxpggdozgp7n6q                                                                                                                                                             
==> Creating release                                                                                                                                                                          
Error You ran into an error connecting to the Fly API. If the error persists, keep this request ID to help Fly Support track it down: 01GBF8ZSX24SGR3A1G247HJ65V-fra