My friend has sent me a message on LinxApp but I can't see it.

When a user first sends you a message on LinxApp you must accept their message request before the conversation appears on your main screen.
From the main screen click on your profile photo in the top right hand corner.
This will take you to your profile menu.
Select ‘message requests’ from the menu.
From here you can see your pending message requests.
Click on a conversation and send a message to accept the request.
This conversation will now appear on your main screen.