To allow WAN Ping on the Draytek 2862ac you will need to access the router interface through a web browser. To do this make sure you're on a device that is connected to the router, open a web browser, and then type the IP address of the router (192.168.1.1 by default) into the address bar then press enter. You will then be asked to log into the router.
Once logged in navigate to System Maintenance > Management. On the Management page you will need to untick "Disable PING from the Internet".
Once you have made the changes click OK at the bottom to apply them.