Whitelist usernames in offline mode

Solution 1:

First, you should not run your server in offline mode.

However, if you have to, you need to add whitelist entries by UUID and not by name. Because server automatically looks to Mojang.com for UUIDs by the name you wrote. So it will be always online=true UUID. Online UUIDs =/= offline UUIDS.

All you need is to get offline UUID, there are some webpage tools for that, for example our servers have this tool on webpage, : http://tools.glowingmines.eu/ , or you can let the people login and you can see their UUID in console, or they will generate their own player.dat in format of UUID.dat in world folder.

However in offline mode, be sure you have some another thing to protect your server, because any pirated launcher can change name of player, so anybody with the correct name can join. Typical use for that is AuthMe.

Note: you did not wrote your minecraft version, so I assume you use newest or at least NOT TOO OLD one.

Note 2 : Capital letters do NOT matter in UUID generation.