Visual Voicemail not working after OS change

[doomedtx]

My wife's 1+9Pro has a NET10 AT&T sim. After years of working successfully, the visual voicemail wasn't available after changing the OS from Oxygen to LineageOS. It took about 24 hours for RCS chat to verify the number in Google Messages, but weeks later the VVM is still stuck on "Activating Visual Voicemail." I've tried turning it off and on without success. Some internet posters say it's required to install Magisk to make the Google Dialer a system app, but I'm wondering if there's a way other than Magisk.