When paid by user insert the details in the table.
Let us suppose three people paid the payments and are added in the following table
UserId, FileName and PaymentStatus.
1 ABC Paid
2 XYZ Paid
3 SKY Paid
Now, at Main page how we check the UserID and How it will work when download button will be clicked by the user, then check the payment status for the file As there are many users paid the payment.