This error message is showing because you haven't submitted the Game ID (Game username/tag) for the tournament (Game) which you're trying to join.
You need to go to Edit Profile and then click on 'Game ID' to submit your Game Username/Game Tag.
Please click on the button below which will redirect you to the 'Edit Profile' page:
Note: Once your Game ID has been submitted and you want to get it changed/updated, or you want to get your Email/Mobile Number updated, it can only be done by the Admin Team. Please click on the chat button as shown in the picture below on our website for Admin Support: