Consider it part of the challenge?
(not affiliated, just a happy customer)
Here's my main.py and Dockerfile[0], if you feel like taking a look. The monitoring tab of fly.io didn't show any errors, or anything like that. Maybe I'm missing something obvious, but I can't really see what the issue could be.
Beside that I think Protohackers is an excellent idea.
Luckily, for Protohackers you can use a really basic setup. I used Hetzner’s standard Ubuntu image, opened the nano text editor on the server, copy-pasted my Python code, then ran the program using the OS’s version of Python. Didn’t even run it in the background; just started the program and closed it when Protohackers reported the tests were done.