I had this issue and found different reasons why.
Like mentioned above, make sure your software is up to date. If you have a real computer I recommend the software DJI has to update all your equipment. I’ve read both “yes“ and “no” to battery updates. Apparently other DJI drones require battery updates, while the Mini does not. I cycled through all 3 of mine while my Mini was connected to my PC just to be sure. I didn’t see any updates.
Another solution was replacing the props on the rear motors. Why just the rear? That’s because the Fly More case for the Mini is a bad product. Long term storage of the Mini folded up results in pressure being applied on the rear props which flattens them out. More flat = motors turning faster to create the same amount of lift = error code on DJI Fly app.
I confirmed my software, changed my rear props, and do not store my Mini folded up anymore. Since doing those things, I have not received that error code.