I have a real problem and it may not be an easy one to solve.
I hope I can explain this clearly.
I have a number of PHP pages which perform the following tasks. They are all within an iFrame.
Step 1) Page_1.php Takes the customers payment then presents Page_2.php.
Step 2) Page_2.php Provides a Paid Receipt and a link to Page_3.php
Step 3) Page_3.php Presents the customer with the merchandise then sends the customer to Page_4.php
Step 4) Page_4.php Summarizes the sale & provides delivery information then refreshes to the LogIn.php page.
Now here's the problem.
That is a BIG TIME DISASTER!
Because on Page_3.php the customer then can get the merchandise again without paying for it the second time!
This allows the customer to get/steal FREE merchandise each time the customer clicks the Browser's BACK Button. The customer can do this all day long!
How can this be prevented?
I know this is a tough challenge to solve, but I'd appreciate all the help I can get on this.