Invalid session often requires refreshing the Launcher session. First check the player session without changing the server's authentication settings.
Step by step
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Close the game and Launcher completely. If there are any other instances of Minecraft left open, close them as well.
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Check the Microsoft account used in the official Launcher. If necessary, log out of your account, log in again, and launch the gaming profile using the same account.
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Verify that internet access and device time are correct. Compare if the same error occurs on another known online server.
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If multiple players are affected at the same time, the administrator should check the authentication service and server logs. If only one account is affected, focus on that account's session.
Keep in mind
Turning off authentication removes the protection that checks ownership of the player name. Don't use it as a general solution for this error.