What license does this project have? A license is technically necessary for legal reasons. See this stackexchange post
In short, the only thing you can safely assume is that you have no rights to do anything at all with this code.
Looking at some of the source code, I can see that some of it seems to be copied from the Stripe plugin, which is under GPLv3, but some of the files do not have a header indicating the license. I'm not sure if copying the basics of the Stripe plugin would count as a derivative work.
What license does this project have? A license is technically necessary for legal reasons. See this stackexchange post
Looking at some of the source code, I can see that some of it seems to be copied from the Stripe plugin, which is under GPLv3, but some of the files do not have a header indicating the license. I'm not sure if copying the basics of the Stripe plugin would count as a derivative work.