JiaJue Stiff Gearbox lever

Hello Friends, I bought my son one of these JiueJue or Sonic Motors N10 250cc motorcycles. Unfortunately after only 33 Km we are having issues with the gear box. Suddenly the shift lever is very stiff and does not go through all the gears. We took the gearbox case cover off and all seems fine and new. The springs on the actuating mechanism are ok and in place. Clutch is actuating. Any ideas whats wrong?
Any remote chance I can get a service manual?


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