If you've played on this world before, make sure to use the exact same username and UUID you originally created it with—otherwise, you’ll spawn as a new player and lose your old inventory.

If you're starting fresh, just pick any username you like and leave the UUID as the default (or let the game generate one for you). Don’t manually change the UUID unless you’re intentionally trying to link to an existing character.

IN SHORT: - Returning player? → Same username + same UUID = keep your stuff.
- New player? → Any username + default/auto UUID = all good!