Prius key cannot unlock the door

I bought this car from facebook marketplace at 160k miles. 2014 prius.

There was a period where the battery died so the doors could not open.

And the physical key could not open the drivers side of the door, no matter how hard I tried. So I had to call AAA to open it up for me.

The AAA guy said that it's common for people to swap out the key sets in cars/key fobs because its common for them to be stolen.

Is that true? Or do I need to lubricate the keyset (though seems unlikely)?

If true, what is a cheap way to replace the key set?