The F50 error code indicates that the machine control board senses that the drive motor has stalled. It is detecting no motor rpm's from the rotor position sensor on the drive motor. This can be caused by a friction problem. See if your basket inside the tub spins freely. If not, check for a foreign object underneath the washer that could be restricting motor movement.
An item stuck between the basket and the tub of could also cause a friction problem. You could have a mechanical failure or a wiring problem that is causing this fault code. A problem with the machine control board could also produce this code.
If you cannot find and correct an apparent friction problem preventing the basket from spinning, then I recommend calling a service technician to diagnose and repair the washer.