[Hall of Famer]

First of all, !empty() can be used to replace is_numeric(), but I am pretty sure the redeem.php has !is_numeric(). See the difference? ! means 'not', so it is the opposite to is_numeric(). Of course it wont work if you change !is_numeric() to !empty(), it should be empty() instead.

I also do not recommend you to change every is_numeric() to !empty(), unless all your table IDs are alphanumeric. If the trade id is still numeric, you are better off just leave the code the way it was.