Hi… Whitelisting would require static egress IPs:
https://fly.io/docs/networking/egress-ips/
Also, there’s a more convenient variant of this in beta, which removes many of the shortcomings of the per-Machine addresses mentioned in that doc…
https://community.fly.io/t/beta-feature-try-out-app-scoped-egress-ips/26536
Hope this helps!