So we've migrated to the Pro plan because we need a static IP so our services can be whitelisted by a customer's DB. But to our surprise, our service is receiving a connection timeout even though the service is already whitelisted.
So I tried connecting to the service manually to check things manually:

1. The IP when running curl -s [ipinfo.io/ip](ipinfo.io/ip) in the shell matches the static ip from our service.

2. Running sqlcmd manually through this same shell will also result in a denied connection (timeout).

The only conclusion I could reach is that the IP is not used when connecting via TCP, but I couldn't find this specification in the documentation.

OBS: And of course, when running the service or the sqlcmd through a local whitelisted IP it works as intended, so it's a problem related to our railway environment.
OBS2: Also, I asked our customer to check again if the IP is correctly set on their system and I am currently waiting for a response while I am writing this ticket.