Arrears
“Arrears” is money that is due but as yet unpaid. Technically, you’re in default.
Contrast with in arrear, which means “payable retrospectively at the end of a given period”.
A bit of a pedant’s trick for young players, I grant you — but mildly diverting on a slow afternoon. Plain English Anatomy™ Noun | Verb | Adjective | Adverb | Preposition | Conjunction | Latin | Germany | Flannel | Legal triplicate | Nominalisation | Murder your darlings