my Xbox has stopped receiving notification

If you mean party and game invites? I would check if it's working now as there was a service issue yesterday:

https://twitter.com/XboxSupport/status/1416615773607383041

Message notifications with my Windows 8.1 phone on my Xbox One hasn't works for a few months for me. One day, the notifications simply stopped. My son has an Apple phone, and it works. I find that pretty funny. Yes, I reinstalled the app. Notifications simply
died.

I am also having this issue, as well as a friend of mine. I have tried turning select notifications off, such as group and party notifications. My friend has tried turning notifications off entirely. Neither attempt to stop the notifications has worked.

This has nothing to do with redeeming a code. The points are still in my account and I’ve received no further notification from Xbox.

Yeah, I have the 640. My notifications stopped around March, and I still haven't got it to work again. Now I only use smartglass if I'm on my Xbox, and receive notifications on the console. I'd much rather message people with my phone's keyboard which is
the only reason why I've kept SG on my phone at all.