T-Mobile Conditional Forwarding Fails. T-Mobile network reads my GV # as Invalid

I am following the steps correctly as have done with my other T-Mobile line. So the issue isn’t the setup:

• Phone/Dialer -> Settings -> Supplementary services -> Call forwarding ->
• Always forward = Off
• Forward when busy = +1[Google Voice Number - including area code]
• Forward when unanswered = +1[Google Voice Number - including area code]
• Forward when unreachable = +1[Google Voice Number - including area code]

I did several test calls, and when it transfers to the Google Voice number it hangs up immediately!

I change the forwarding number to my other Google Voice Number (the one I use for my other T-Mobile line), make a few test calls, and it works perfectly!  The calls were seamlessly sent to my GV voicemail, and the messages showed up immediately in the Google Voice app.

I spent HOURS on the phone with T-Mobile tech support and they are telling me that the number shows as invalid in their system though they confirmed that the Google Voice number I am using IS valid and IS linked to my T-Mobile cell number.

I already have my work Cisco voice number forwarded to my Google Voice number, and it works (rings though to the Google Voice app on my phone). So I am at a loss why T-Mobile’s network reads my Google Voice number as “invalid”.

What can I do here??