Dumb question about custom text sounds

[biotron2000]

I receive a lot of MMS notifications from email addresses that do not have phone numbers attached to them. I've used Textra for years, and it allowed me to set custom notification sounds for these senders. I wanted to try the Samsung text app, since Textra does not work with the Live Message feature (the GIFs never go through. Same with Android Messages, BTW).

Even though I have assigned custom sounds to these senders' contacts, the default notification sound plays. For contacts with phone numbers, the proper custom sound plays, at least when the messages are sent using their numbers.

Am I missing something? I've tried setting the email address as the phone number, to no avail.

Barring a resolution, has anyone been able to send Live Messages with Textra?

Thanks!