Or that the problem is with the proxy?

If you connected a proxy and suddenly notice that the site you need right now does not open, what will you think first, that the problem is with the site? Or that the problem is with the proxy? To avoid guessing, proxy providers offer different testing tools, including this checker https://floppydata.com/website-checker/. It is the most optimal and fastest way to check everything at once and quickly figure out where the issue actually is.