I've written an open source library for iOS, and I've received an email from an overseas developer who wants to pay me for my work so that he doesn't have to attribute in his app.
The code is released under the MIT license, which allows for reuse so long as the license is distributed along with the code. I told him that he can just use it without attribution, but he insists on sending me something.
What's the practice in the open source community, bearing in mind that several others have contributed to my library? Is there a standard or convention in the OSS community for this sort of thing?