You should always format SD cards within the device that you are using it in. So, try formatting it within the DJI app while connected to the controller.
It fits inside mine.. without a case. it's a snug fit in one of the side slots, and has to go in before the drone. The slots are foam so they are flexible.
I just laugh at people saying they would not use these. Unless they have some specific info on why these are bad... it's a battery. DJI is not god of batteries.
There is no secret or amazing technology used in the cases made by DJI that make them better than other brands.
I have the DJI brand hardshell, but only because it was free. Otherwise, I would have purchased a cheaper case.