minecraft-java-edition
I don't understand this and I'm now worried as I have donated to a lot of servers and I don't want to lose this account. On the launcher it says my new username but when I log on it says "Account not Authenticated with minecraft.net" and "Non-Valid Username".
How can I regain the ability to use my account online?
Having played on a cracked version before you need to completely uninstall your Minecraft, because more often than not cracked Minecraft versions typically use a proxy to bypass the login phase of the download. So long as you have the old install, your Minecraft will still use the proxy to authenticate. Additionally, a lot of those proxies pair with your actual Minecraft account, so that could present some issues after you paid.
I'd suggest clearing out your .minecraft folder and deleting your minecraft.exe, download a new one from the Minecraft website, reinstall your mods (according to the instructions given by the modder), and you should be good to go.
Make sure that when uninstalling, you don't delete these folders:
These folders all store data (Such as your worlds, achievements, and screenshots.)
If you have just bought Minecraft, you account will be a Mojang account. This means that
instead of using your username (ex: player1234).
In the username field, you will use your email: (eg: player1234@xyz.com).
Source: https://help.mojang.com/customer/portal/articles/823771-error-logging-in-with-a-mojang-account
When logging into Minecraft with a Mojang account (or a migrated Minecraft account), please be sure to use your email address, not your username, and Mojang account password
Best Answer
It's caused by remaining logged in after changing your name. Not everything is updated.
You need to open the Minecraft launcher, log out, and log back in again (i.e. you need to enter your user and password again). This should fix it.