Hello AndyJK,
Thank you for participating in the Apple Support Communities! We understand that your MagSafe charger is no longer charging your iPhone. You've come to the right place for help.
Let's start by ensuring that you're following the guidance found here:
How to use your MagSafe Charger with iPhone 12 models - Apple Support
Specifically, you'll want to connect the charger to a power adapter that's at least 20w or greater. The "Learn more" section provides additional suggestions to try.
If that doesn't work, do you have access to another device you can test this charger with? Does the iPhone charge with other wireless chargers? Is there any change after you restart the iPhone?
Cheers!