使用AJAX的Flask flash和url_for

I am currently stuck on a rather "big" problem, and I will try to be as clear and concise as I can about it. I am developing a tool in Python, using Flask. It's meant to be an intranet. The idea is that I have a client page. There's its name, numerous other infos, and a massive checklist.I am currently stuck on a rather "big" problem,