FIFA21 Xbox - How to Accept an Invite To Play
If you are the away team you will need to accept an invite instead of sending one. The invite will appear along the bottom of the screen. To accept the invite hold down the glowing Xbox logo button. Once you hold it down for long enough you will automatically be taken to the team select screen.
(:20) Don't worry if you miss the invite notification, you can still join your Rival match. You can find the invite in the Invitations tab. To find the Invitations tab, press the glowing Xbox logo button. Next, use the left stick to scroll right until you reach the "Parties and Chats" menu. Use the left stick to navigate down to the "Invitations" menu, and press "A". On this menu, you will see your latest invites. Press "A" on the invitation, and you will be automatically taken to your game.