Wiktionary
a. That cannot be pay.
Usage examples of "unpayable".
His health broke, companies with which he was connected collapsed, mines proved unpayable, and, lastly, he sold a reversionary interest in a considerable sum for a third of its value on the very day before the life-tenant died!
This New Warfare, which the prophets had said would end in a scientific massacre of mankind, passed insensibly into a squalor of political fiascos, unpayable debts, unsubscribed loans, scrapped machinery, insurrection, guerilla and bandit conflicts, universal hunger and the great pestilences.
Aunon, to the faculty and staff of the Department of Electrical Engineering at Colorado State University, and to the CSU chapters of HKN and IEEE, in token payment of the only other kind of moral debt that is essentially unpayable.