“Proxy authentication required” message

A message that says “Proxy authentication required. Enter the password for HTTP proxy etc.” keeps popping up whenever I try to go to a website. My WiFi has no proxy, and has never had a proxy. It even pops up when I’m using mobile data. I have no issues with my iPad, and it’s only when I’m using a web browser. YouTube, Netflix, etc. work fine. I’ve tried restarting my phone, resetting network settings, but nothing works. I’m on iOS 12.2.