Best Choice Twin Tub Washer/Spinner will not agitate

I have a Best Choice portable compact washer Model SKY3489 (purchased from Walmart, “Best Choice Products Portable Mini Twin Tub Compact Washing Machine and Dryer Combo, 18-Pound Load Capacity”) that has stopped agitating on the washer side. With it set to wash, there’s no agitation, but I can reach into the wash tub and get the agitator to start in one direction. It runs for about 5 sec until it reverses direction. Then it stops working. I can by hand start it again in the other direction for another 5 seconds. Then it stops again. It sounds fine. That is the motor is heard operating with a normal ‘hum’. The wash timer also appears to work fine too. Does anyone know what the problem might be? .

I have opened the back access panel and checked the belt. Its fine — good tension, little wear.