I wonder if Fly.io still waves invoices that are less than $5, most part of the internet says so but there seems to be no policy talking about it and also things saying it discontinued after October 2024.
Also mentioned at: Is there still a policy on waiving invoices less than $5? (After the changes in October 2024)
Hi… This counterexample from May says that that waiver was still in effect, so I don’t think the October date is magic:
You’re right to treat it as iffy and not necessarily permanent, overall, though. As just a fellow user, I’d recommend not making any plans that rely on it continuing indefinitely into the future.
You can email billing@fly.io to get the official word on this and any other payment policies, 
. Unlike the other addresses, you do not need a Support plan to send questions there.
Hope this helps!