vpn not connecting on iphone

Q: "My VPN not connecting on iPhone after I updated it to the iOS 13 build. What should I do to make my VPN resume?" - an iPhone user

VPN (Virtual Private Network) is more and more widely used nowadays to protect your privacy or bypass regional restrictions. However, it has been reported by many iPhone users that their VPN not working on iPhone for reasons unknown or known, e.g. update of iOS 13. In this article, we will address the VPN connection issue with the best 7 solutions, which fully support iOS 13.