I’m trying to change my Xbox gamer tag but it says it’s not allowed

Nope this is my first time

Hi There

The following are important things to note before changing your gamertag:

• If this is your first time changing your gamertag, you can change it one time for free. This is regardless of whether we created it for you automatically when you first signed up for Xbox (meaning you didn’t choose it yourself) or if you created your own gamertag at signup.
  

Note After changing your gamertag once, all future gamertag changes require a fee (cost varies by region and currency).

• On Xbox 360: Gamertags can be up to 15 characters long, including spaces. They can’t start with a number.
  
• On Xbox One, Xbox Series X|S, and Windows: Gamertags can be up to 12 characters long, including spaces. They can’t start with a number.
  
• If you receive a message that says a gamertag is unavailable, this means that you’ll need to try another. The gamertag that you’re trying to create is either inappropriate for the Xbox service or can’t be used at this time.
  
• After you confirm your new gamertag, the change is reflected across Xbox. You don't need to tell your friends that you've changed it—their friends lists will be updated automatically.
  

I'm not sure how they would have done it. No one here could do that.

It happened to someone before I’ve seen it myself

If the system says it's not allowed, there's no way to bypass that.