Did you follow the payout motor wiring..
I am not sure which one is the payout motor, I took a video of the wireing, hopefully is clear enough...

So you’re saying it does not pay out at all then if balls are ONLY falling out the back…
The wasted balls drop to the back, the winning ball are paid in the tray, I think it can be seen this video:

https://1drv.ms/v/s!AkkrUeTzpjcKiaJ6...Y7v3g?e=IYydF3

Was it shipped in packing peanuts?
It was shipped in bubble wrap

Sometime the ball launcher doesn't have the strenght to throw the ball, could it be linked to the problem?

https://1drv.ms/v/s!AkkrUeTzpjcKiaJ7...eDqwA?e=JSrGuF