I have added a backup ISP, T-mobile. I am trying to get this working with BI IOS app. While on local LAN, it connects with no issues.
T-Mobile 4GAR gateway is connected to my router thru it's RJ45 port.

Note that this gateway is not a pass thru modem and is a sort of a router. So I have double NAT but that is not an issue. All my devices and IOTs can be externally accessed.

I have verified that the remote external WAN address is correct on the server and the BI IOS App. The key is correct too. However, The APP just saying Connecting and Retrying.

Note that I can connect externally to the server via Chrome RDT which uses a port sort unsolicited port 81 from BI App should not be an issue. I am told that T-mobile stops these types of external port based unsolicited accesses.

Any ideas how to resolve this?
Many thanks!