Hi Sean, it sounds like the FLY_API_TOKEN environment variable may not be set. Try running something like echo $FLY_API_TOKEN | wc or echo $FLY_API_TOKEN | head -c 3 right before the flyctl deploy --remote-only call to see that the environment variable is getting set correctly.
If it’s not set, double check the Bitbucket pipeline secrets to ensure the names/values are correct.