He paid them $40 million.

There is a documentary on Netflix called American Conspiracy. I recommend watching it. It covers how that happened and who paid them and how the Reagan government stole software from a US company and sold it to foreign governments to repay the person that paid the Iranians.

This was just a big scandal, well, it should have been. It was all set up to help Reagan win. https://newrepublic.com/article/172324/its-settled-reagan-campaign-delayed-release-iranian-hostages