Typically, Error 721 occurs when your ISP/Network does not allow PPTP Port 1723 or GRE packets. To rectify error 721, please check the router settings and make sure TCP Port 1723, IP Protocol 47 (GRE) are allowed. Also, make sure that the router has the PPTP and PPTP pass-through option enabled.
Furthermore, you may switch between L2TP, SSTP, and OpenVPN protocols.
If the above information helped resolve the error 721, kindly use the comment box below for your suggestions and feedback. Please use the comment box for your suggestions & feedback. For additional help, please submit support ticket with errors and screen shots (if possible) or contact our 24/7 live chat.