Hi,
It may be that you have a custom relationship with Fly and have obtained a static outgoing IP, however as far as I’m aware it is not possible to get one e.g
However … I’ve also used Stripe. I didn’t need to verify a static IP.
Your app may well have different/stricter requirements however when I did it, I needed to verify the IP that Stripe’s request came from (which is possible because Stripe does have a fixed range of IPs that you can check against). Stripe did not need to know my IP, where requests to it came from.
(You can also verify its webhook signature, which also proves the incoming request did indeed come from Stripe)
Do you have any documentation from Stripe’s site you could share? That may help show whether it is possible.