Inbound client VPN when Primary Wan is offline

Hi Peplink Community- I have a problem that I could solve using the Find my Peplink feature but not having any success. Here’s the scenario - we have a B One5G in Drop in mode and sharing the IP to a customer’s firewall. Their client VPNs connect just fine with the exception of when the primary internet is offline and using a SIM card (TMobile) for their failover internet. I realize that obviously the public IP changed due to the primary being offline but I was under the impression, using that “Find My Peplink” service it would resolve that address and pass through the inbound VPN traffic to the firewall. Is that not correct or is there a better way? TIA

Do you have a static ip from t-mobile?

Yes sir, it’s that exactly.