Facebook assigns a UID to each user and stores it in the database with that number. We also need to know this number from time to time in order to access the game or payment records of our users.
If you know this number, you can tell us this number. If you do not know, you will need to log into Facebook with your account, then click on your profile. You will see the number on the address bar on your browser.
If the number is not available, you can also copy the whole Facebook address by clicking on the address bar in the address bar of your browser and paste it into the message you will send us.