Cannot receive Whatsapp verification code via SMS or Voice Call on iPhone

I don't receive a verification code via SMS after downloading Whatsapp, and when trying the voice call method it routinely asks me to "enter 9 to receive verification code" and when I do the call goes dead (beep beep).

iPhone 15 Pro with T-mobile - I receive all SMS and voice calls from others just fine. T-mobile reset my network settings to no avail, and I've read countless online support/suggestions to no avail.

I'm getting the canned responses from Whatsapp support. Any ideas?

I thought maybe forcing the "voice call" option to voice mail might have them provide it to me automatically but the voice mail stops after it asks me the same thing when I'm on the phone, "enter 9 to receive verification code."

Can't understand why this particular SMS verification isn't coming through…