Moved to Venture X from Amex after 23 years and racked up many miles already and it was ready to transfer miles to upgrade my flights for holiday trip, i could not log into convert rewards section. After calling the customer service, they've explained to me that if the device my phone was associated with is recently upgraded (i did upgrade my phone 10 days ago from iphone 13 to 15 with ATT), i will have to wait until ATT updates their identity records.
So i cant transfer my miles, Cap 1 does not know how long it takes carrier to update their records (also being 18 years ATT customer, so weird that they need to update my identity). Basically what I have learned was that due to a lot of IMEI, Phone Spoofing going on and converting miles from cap 1 to external entity has not reverse option so cap 1 added that additional identity verification which sends out SMS to your phone. But if you recently upgraded or got a new device, the phone number and Name has to match in order for 2FA to work. So when they are trying to send SMS to phone for verification, the name does not match since it is a new device.
What I have been told is until ATT updates their records, i cant transfer miles. It is so surprising that Cap 1 does not offer alternate 2FA like authenticator or some sort. It is in the loop of not sending message and no explanation of why it is not working.
I think Cap 1 should not rely on carriers to update their records and come up with their own verification method if the SMS does not work. It is so frustrating, i am traveling in 2 days and my plan to upgrade my tickets to business class with miles i had. I cant do it.
If i knew this was going to happen, i would have waited until after transferring miles to activate my new phone. It is plain stupid.

Yes, it is on eternal loop.

Mine is also a few weeks now and still not working. Planning to call ATT

Not sure how it worked for you. I want to post the screenshots but system is not allowing me,

Called ATT and they have no clue why this is happening but not sure how long will it take for them to update my identity for the device i bought from them and being their customer for over 18 years. It is so frustrating.