I have a Bafang 750W fatbike motor. Bought it in 2016, so it's been around. Mine uses a freewheel, not a cassette.
I went back and looked again at cayjack's issue with his Radmini. He couldn't get the nut/washer off. I don't know why Radmini did that, but they flipped the motor connector around so the bigger side (female pins) is connected to the motor, and it won't pass thru the 12mm nut/washers. He had to split his freewheel tool. Grinding down the nut/washer does not seem wise to me.
My Bafang motor, and all the rest of my motors puts the smaller connector (male pins) on the motor side and that allows the axle fasteners to come off. It also passes thru my Park FR 1-3 tool.
You will just have to see how your fatbike was put together. I also believe you can buy a tool from RAD for not much money that will work if you have the hub with the nuts that won't come off.