Felt bad for not tipping

I went to a new nail salon and got my nails done along with my brothers new girlfriend and her friend on my brothers dime. My little brother told me to not worry about the cost and so even though we tried to keep things reasonable the salon was expensive and we ended up spending $150. I was definitely going to leave a good tip since their service was good but when I went to pay I noticed a bunch of flyers up that said they don’t accept tips off of debit cards, cash only.

The service was good but slow so by the time we were done we needed to go do the girls could get to the boat trip he had planned on time, I did not have my own money to spend muchless could I even afford to. I honestly don’t have money outside of putting food on the table and I’m stressing about how I’m going to even pay rent. So I felt really bad but there was no way I could leave a tip.

Is this a common practice with nail salons and cash only tips? Or is that place kinda screwing over their workers?? (I rarely get my nails done)

I work in a tip dependent industry so It felt awful leaving without tipping, but there was nothing I could do.