What is the ruling when a claimant alleges a debt or right, and the defendant claims the claimant has absolved them (Ibra') or fully received payment (Istifa')?

Primary text

The statement of the one denying the absolution or fulfillment is accepted, contingent upon their oath. The required oath is to swear by Allah that the right, specified clearly so as to be known, has neither been absolved nor has the claimant taken its equivalent, or that the defendant's liability concerning that right has not been discharged in whole or in part.