New Westwood 50'' 25hp V Series Belt to PTO comes off?

I have a brand new machine but Belt to PTO keeps coming off. Is this set up or a fault ?

The obvious thing i guess is to have it slightly tighter but do not want to pass an unnecessary stress somewhere else to the machine.

I have supplier coming out....also the power lead which enable to open the grass net keeps coming detached...I am not an expert but the lead looks marginally too short.

Has anybody else experienced similar and or rectified?? Thank you,

Paul Barnett
March 2015