I noticed in the readme that you have a parameter organization. I wanted to use this for a personal project board I had, which is not under any org. When unspecified, it defaults to my username (cp2004) however the action seems to fail.

The error also seems to indicate organization-only:

gh: Could not resolve to an Organization with the login of 'cp2004'.

https://github.com/cp2004/github_management/runs/7776329997?check_suite_focus=true#step:4:65

Is that the case or have I broken it? If that is the case, would you consider making it work with both or putting it in the readme?

This add to project action allows to specify the URL, rather than separating the org/project ids, and it works OK.