Hi… I was able to ping that address from a Fly Machine in ewr (NYC), so you may have just ended up with an egress IP that has a low reputation with that particular provider, etc.
This is your ingress address, incidentally; on the Fly.io platform, that is distinct from the one that you use to make outgoing requests, . (This surprises a lot of people.)
I would try just making a new machine in a different, nearby region (e.g., syd or nrt) and see whether that fares better…