If you are trying to use the coupon in the Princess book, you only need to ‘play’ $20, whether you win or lose is not the point of qualifying for the coupon.
Sometimes the cashier will not even check if you have gambled at least $20, but you are mistaken believing you need to lose $20 before you can get the $10 free play coupon added .
Well then I was right & they were wrong as I played quite a bit but was never down by $20.