Mobile lancom Client can't connect

[pfsenf]

Hi,
we are going to establish a vpn connection between a lancom mobile client and a customer network.

lancom mobile client -> pfsense – (inet) --> lancom-router -> customer network

The lancom client is a software tool for managing vpn connections.
As protocol it uses ipsec with nat-t encapsulation.

What rules should I apply on the pfsense especially on the lan and the wan side.

Currently Im a little bit confused because I already have opened several ports but it still does not work.

Is there a general rule what services and ports definitely have to be open.

sorry for my English

I appreciate any help
Thanks