Neither, both ideas seem to have arosen in jewish environment indeed, but i think they shouldnt be connected or mixed up with the idea of "financial debt towards God", as well as the former opinion that it was a debt to satan was mislesding.
I cant imagine that the jewish christians thought generally of God in such a manner, that god quantifies sins, failure, guilt as" debts " on an account or on a scale.
That atonement sacrificies were an back-payment for someone failures or a legal judicial act to justify or satisfy God, than it was a misinterpretation or could have been meant metaphorical.
Redemption could also be metaphorically explained as backpayment, whereas it means redemption of sins on not of debts, jesus redeems from a sinful way a way of mental slavery not slavery of an inherited debt weight.
Atonement was used because becsuse for many jews the atonement day in the temple was in good remembrance, but it was clear for everyone that the sins were ritually symbolicly covered and without forgiveness between parties everything was useless anyway.
At Jesus time mainly Sadducees would insist on a literal adaption and use the thora and sacrificies and put emphazise on the "atoning"and the "arc of the covenant"..and its hilasterion. What I should check whether they used the "debt" Metapher already than.. Pharesean would like to explain the matter more as forgiveness but either not of a debt but more of a sinful behaviour referring more to the prophets and not to leviticus, would be interesting to know how the Essenians thought about it
God then didnt want anything back, but if someone sinned = chooses a way against his conscience, god wanted repentance of hearts. God didnt want a human sacrifice but human hearts that sacrifice themselves,
Jesus had such a sacrifing heart, later that was described "gave his life for us", and if we love someone we will have to sacrifice something mostly. So Jesus death was a symbol that love vindicates anything evil.
So i think this could be how a merciful gods thinks about backpayment, redemption or atonement or forgiveness.