TP-Link mesh system with T-mobile gateway

I have the new 5G T-Mobile Home Internet Gateway hooked to a TP-Link Deco M5 mesh system.  The mesh system has been working fine with an xFinity modem for years.  The T-Mobile Gateway/Deco M5 system appears to work fine for all things Wi-Fi EXCEPT I can't make or receive Wi-Fi calls on my T-Mobile handsets (iPhones).  The Deco M5 system (and another Deco M9 system in another home) have always worked fine for Wi-Fi calling.

I’ve been working with tech support off and on for a month and they haven’t been able to identify the problem or come up with a fix.

Any suggestions?