Establishing an inbound VPN

Hello everyone,

Just looking for some assistance here. I am trying to establish a VPN connection inbound to a Netgear LB2120 Firmware: M18QW_v07.05.170721 (Telstra 4G LTE - Bridged Mode with VPN passthrough turned on) connected to a Synology RT199ac Router running VPN Server Plus with out success; if anyone has been able to do this, can you please advise what configuation was used?, thank you!