Ikev2 VPN on WatchGuard T20 with Flutter_vpn. Strange behaviors

[pizzaandspaghetti]

Hello everyone,
I am trying to use flutter_vpn with a flutter android app that needs to connect to an Ikev2 VPN configured on the WatchGuard T20 firewall.
I can connect and disconnect without any problem but when the code needs to make a call to a webapi the call returns with a timeout exception.
You may think there must be something to configure on the firewall but the strange thing is that if I make the connection with the StrongSwan app instead of via flutter_vpn any webapi call works correctly.
I don't know what to do anymore.
Any suggestions or any thing that can help me?

Thanks in advance!