Applies to: Minecraft Java on the Gravel Host Panel · Time: about 2 minutes · Difficulty: Beginner
The "Failed to verify username" error means the server is checking accounts with Mojang and the player's account did not pass, usually because they are not on an official (premium) Minecraft account. Allowing non-premium players turns that check off.
Servers that allow non-premium accounts are easy targets for griefers, because anyone can join with any name. Turn on the whitelist and use a login plugin.

server.properties to edit it.
online-mode=true and change it to online-mode=false.Join your server. The error no longer appears.
Still stuck? Our team is on Discord, or open a ticket from the Billing Panel.