Trying to update my payment methods and it keeps saying my payment method isn’t valid. I’ve been using this vida for years

I think you might be best served by removing the card and adding it back again as suggested.

You can also try editing the payment information here, rather than in the settings on your device.

https://appleid.apple.com/account/manage

Be certain its data is current, correct, and complete.

Perhaps, for example, it expired.

Remove and re-add it if necessary.