Prime won’t charge, “plug in charging system malfunction” message on screen

Try the charger that came with the car to eliminate your L2 EVSE as the problem.

 

^ Yep; you need to isolate the issue. Is it your car or the charger that's malfunctioning? If you don't have the OEM charger, use a 'known good' public charging station. They're usually readily available at libraries and gov't parking lots around here.
Also look at the charge socket. If you forceablilty plug-in the car, you can bend or push back the electric contacts. I'm guessing you probably have a ground fault issue; which is most likely on the car side.
The EV portion of the car is classified as part of the emissions control system; so you can make the argument that it should be covered under the federal emission standards; I believe is 8 year or 100K miles. That's the reason these cars got state and federal rebates. This is dependent on your dealership, but you should be close enough for a customer satisfaction waiver. Just be kind but firm, if the problem is in the socket - they could argue that you broke it with the non-OEM charging unit.

Good Luck.....

 

I had the charger that’s built into the car go bad. They replaced it under warranty. I can’t remember if an error message showed or not and didn’t result in a ground fault.

 

You can usually recognize a ground fault by watching the flash codes after plugging-in. If it's a bad socket or ground fault, I doubt it would light-up the CEL; not a primary systems operational fault.
Your the first that I've heard with a failed traction pack charging board. Did it throw the CEL and did your force charge button function?

 

I can’t remember if there was a CEL. There probably was. It just wouldn’t charge from the EVSE. It ran as a normal hybrid otherwise. I drove it as such while waiting for the part to be ordered.