I'm a grad student in the United States with a strong programming background in a field where most people have very little programming experience. A while ago a faculty member I know requested my help; they were working on a manuscript for an analytical framework with major applications, but needed someone to implement it in software because it addresses very computationally difficult problems. By creating a somewhat performant proof-of-concept to go with the manuscript, and contributing to the manuscript in other ways, I got to be a coauthor, and it was published in a very high-tier journal. I then developed a complete software package that has been published under my account on Github, and then we published it as a software note with me as the first author in another pretty decent journal.
Currently, I'm the sole developer of the software. It's fairly complex and unlikely I'll be able to find someone that could pick it up. I still like to maintain it and add features to it because it has cool applications and I want to see it be used and be successful. The problem is, writing and maintaining good software (which my field desperately needs, and is what I would like to do career-wise) is very time consuming, and it's harder to justify taking time away from other things to keep it going now that the manuscripts (e.g., more tangible rewards) have been attained. I was thinking of adding a donation link to the bottom of the main page on github for the project as a way for people to show their support for the project. As a grad student, even a little bit of extra income (and I know enough about funding in the open-source community to not set my expectations high) would be a huge help, and would make it easier for me to justify spending my personal time on it.
The question is, are there any ethical concerns with doing so? I mainly did it as a favor and a way to get my name on some good publications, so it is an academic project in that sense. With that said, it was done in my personal time without university resources.