niepłatny in English:

A promise made is a debt unpaid.

For many young graduates, starting out in a new career means taking an unpaid internship.

Any extra holiday will have to be taken as unpaid leave.

Their days off are unpaid.

We have several unpaid helpers at the school.

My unpaid liabilities are still $100.

My telephone service was cut off because of unpaid bills.

He was sentenced to 200 hours of unpaid work.