I ran into a similar kind of situation with a rental car in Mexico City. Was pulled over by the traffic police. Between my poor Spanish and the traffic cop's poor English I finally figured out he pulled me over for an expired registration tag. Sure enough, the tag expired at the end of diciembre and here we were in enero.

He basically told me that the car couldn't be driven with expired tags. Knowing how things work in Mexico, I asked him what he suggested. He said call the rental car company which I did. They talked to the officer, some negotiations took place, the phone was handed back to me and I was told to pay the officer the equivalent of 25 dollars to make him go away. They'd reimburse me when I turned in the car.

Done.