Facebook Credits API PHP - Update user_id in mySql database after purchase

I have an app where I want users to be able to buy in-game credits called coins.

I have set my callback url, and can make a purchase, I get an order_id and settled from the callback, but how do I update the use开发者_StackOverflowrs row in my mySql database after they have made the purchace.

Kinda how my mySql DB looks

ID......FBID............Name..........Coins

7.......1000***797....John..............0

After the user has bought 200 coins for 1 credit, I would like to do this

$SQL = "UPDATE tb_users SET Coins = Coins+200 WHERE FBID = '$usernumber'"; $result = mysql_query($SQL);

But how and where am I supposed to do that? Is it in the callback.php file or in the index.php file after "var callback = function(data)".

I can't seem to pass the user_id from the form on the index to callback.php

So how do I do that, and if that is possible, am I supposed to update my database in the callback.php file??

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Nevermind found this out. You can get the info about the user via API the normal way and update the DB in callback.php after "settled".