“Inspired” is not an honest term. You’re using someone else’s code, so abide by the license they use, or remove their code from your project until you’re ready to follow the license. You started lifting Postmill’s code several years ago now and have had sooo much time to set things right but keep dragging your feet.

This isn’t a school project, you’re gaining financially from someone else’s hard work without abiding by their (incredibly permissive) FOSS license and opening yourself up to serious legal action.