There is a reason why just about everyone is moving away from cash some of the many being
1) No need to carry a float
2) Speeds up the on-board service, No need to provide change, and/or the issues of not having the correct change.
3) What currency do you accept on what flights ?
4) If not native currency there is the issue of paying FX fees
5) It stops theft, there is no cash to steal.
6) It massively reduces the time to do reconcillations
7) Saves all the logistics involved in getting the cash securely off the plane, storing it elsewhere and then getting it to some central point.
8) It saves the bank charges
9) negates issues of accepting fake notes,so in fact there are "issues with not getting paid", when using cash.

All for an ever decreasing minority that would want to prefer to use it on a flight.