EX15W Can't access the management GUI from LTE Modem Public IP

I have a EX15W configured up and running. It is currently set for a backup ISP using an LTE modem connection with LAN1 port connected to WAN2 on a Ubiquiti UDM PRo.
For whatever reason I can’t access the Digi Management GUI portal via the public IP of the LTE Modem (External).
Even when I have the DIGI working without the UDM connection I still can’t get to the GUI.
I have already added “External” on the Digi ACL.
Any help would be great. thanks.

In order to have remote access, your cellular account must either have a Public IP address with 2-way communication (sometimes referred to as Mobile Termination), or it must be a Private IP address that is reachable over a Private APN provided by the mobile provider.

You should also configure your APN within your EX15W. If needed, here is a link on how to do that: Digi EX15 User Guide?

If, after checking on the above, you are still having issues, please open a Tech Support case by emailing us at tech.support@digi.com.
please ensure you have both cellular antennas on your EX15W, make sure it has been powered up for at least ten minutes (with the APN configured), and then gather the Support Report. If needed, here is a link on how to generate and download a Support Report: Digi EX15 User Guide?

Please let us know.