Wi-Fi Calling not working on US Mobile

I'm new to US Mobile and had plans to port a bunch of lines over. I got the first one ported from Cricket and am stuck with not being able to get wi-fi calling to work.

The phone is a Samsung S26+, Spectrum branded but unlocked. The wifi calling option shows up just fine when on a Spectrum eSIM but as soon as I switch to US Mobile, the wifi calling option completely goes away. I tried both Warp and Dark Star. T-Mobile/Light Speed does not have towers in my area.

I then tried the same line with Warp on a Samsung S23. This phone is also Spectrum branded but unlocked. Wi-Fi calling works on here for both Spectrum and Cricket, but again, when I switch to US Mobile the wi-fi calling option is just gone. It seems strange that wi-fi calling works for 2 different providers but not US Mobile, so I wonder what US Mobile is doing differently here.

Customer service has not been able to help. Due to poor reception from all carriers at my location I need wi-fi calling. If I can't get it set up then I won't be able to use US Mobile. Does anyone have any ideas to try? Thanks.