Is it permissible to work for a car rental company if the majority of its capital came through "organized Tawarruq from the Saudi Fransi Bank" (with the company owner being unaware of the prohibition of organized Tawarruq), and does sin befall the accountant who records the payments of this loan?

Organized tawarruq is forbidden, according to a resolution by the Islamic Fiqh Academy, which described it as the bank selling a commodity to the mustawriq (the one seeking tawarruq) for a deferred price, on the condition that the bank acts on behalf of the mustawriq in selling it to another buyer for an immediate price. However, as long as the company is unaware of its impermissibility, there is no sin upon them if they did not neglect to inquire. And there is no objection to you working as an accountant with them and recording the payment transactions of the previous deal.