L2TP-IPSec server

Following the instructions from Manual:Interface/L2TP for L2TP/IPSec setup, I have run into what I think is a firewall problem.

The reason I suspect this is because I can connect to the VPN server fine from inside the network, but not from outside.

Here’s the ports I opened:

add chain=input protocol=udp port=1701,500,4500
add chain=input protocol=ipsec-esp

Is there something else I need to do?