Xbox 360 Backwards Compatibility Error 8015190A

Hi Microsoft,

I recently picked up an Xbox Series S and got everything setup and working fine. I wanted to bring along my 360 collection, so I plugged my old console in and started transferring my saves into the Cloud. I managed to move everything across however towards
the end of my process, the 360 signed me out of Xbox Live and wouldn’t let me back in.

Since then, I’ve consistently been getting errors trying to sign-in to Xbox Live with any 360 device, including my physical 360 and the Series S in back-compat mode. The error is always:

Sorry, there is a problem with the credentials you’re using to sign in. Go to https://account.microsoft.com to fix the problem.

8015190A

I’ve tried multiple solutions now, none of which have made any difference, including:

* Removing the profile from the device and re-downloading

* Updating my Xbox Avatar

* Creating a new app password (I have two-factor enabled)

* Switching two-factor off (and on again)

* Checking enforcement status - account is in good standing

* Checking account profile - no outstanding security / account warning

* Check Xbox Live status - Showing my subscription to Game Pass Ultimate in good standing

I’ve run out if things to try. I did notice that when I check my Account Activity, the sign in attempts from my 360 & back-compate modes never show up, so it appears as though I’m never getting as far as the device even registering the authentication attempt.
The Series S logs in fine and I can sign in everywhere else with both two-factor and app passwords, so it’s just the 360 services that seem to be the issue.

It doesnt appear that I have the option to contact support from the website, so I’m at a loss for things to try. Please help!

Thanks!!

:)