Check if there is a service outage. If so, it would be reported in the following sources:
 
@MojangStatus on Twitter
PlayFab Status
Xbox Live Status
 
If an outage has been reported, you will need to wait until the outage has been resolved. If no service outage has been reported, you may need to verify the following:
 
Please make sure your game is up to date and running the latest version of Minecraft.
Make sure your Minecraft account is linked to a Microsoft account. You can check this by going to the main menu, then clicking the sign-in button at the bottom right.
 
After confirming the above, please complete these troubleshooting steps: 
 
Check your internet and ensure your device's connection is stable and strong. 
If your issues are caused by the internet connection, you may need to reach out to your Internet Service Provider and/or complete separate troubleshooting steps. 
Sign out of all Minecraft accounts including the attached Microsoft account and close out any open Minecraft application. 
Restart the game, then sign back into the Minecraft and Microsoft account(s) 
If you still see the error: repeat the steps above after waiting 1 hour, including internet troubleshooting steps.
 
If this issue persists, please wait 24 hours and try these steps again.
 
After waiting the 24 hours and repeating these steps, please report this issue in the bug tracker.