Hello Colin George,
Thank you for reaching out to Microsoft Q&A forum
I understand the system won't recognize your payment details to resubscribe to Microsoft 365.
Here is what you can do:
Make sure to remove any old payment method completely
It is recommended to remove any expired cards before adding a new one.
- Sign in to Payment options
- Select the old card > Remove
Payment issues can sometimes cause by cached credentials or outdated cookies in your browser.
- I suggest try a different browser or go into private/incognito mode and try to resubscribe from there.
Here is also a site that contain info about many issues when trying to renew Microsoft subscription, please refer to it in the link below, it may contains helpful info:
Problems renewing a Microsoft 365 subscription
Feel free reply back to this post if you need further assistance, I'll be happy to help.