'Cash from debtors' means any income that a business receives from account customers that are sent an invoice, usually at the end of the month. After they have been sent an invoice, they are referred to as debtors. When they pay the bill, the payment is referred to as Cash from debtors.
Although the majority of arcade businesses don't have any debtors, it's possible that you'll make your arcade available for exclusive hire - for example for a children's birthday party - and offer account terms to customers who hire it. (These could include private individuals as well as other businesses such as party planners.)
Don't forget that the Gambling Commission Code of Practice for operators of family entertainment centres and adult gaming centres does not permit credit to be provided in connection with gambling.