Thanks
Found out the problem, ES Explorer was acting out
Just stop the program and the usb will mount
Then using kodi, enter file manager and enter root folder Inside there’s a folder called storage
There are two folders inside one called self, and the other one called emulation
The other one (if it appears) is the usb drive 😀
I'm not near my unit but USB storage is read only with Android 6 on Mi Box.