Hi Jason I implimented the code you stated (had to change the else statement a little as it came up with a syntax error.
Its not working though, as when i click the button to go to checkout page it automatically sends me to the success.php page and comes up with this error:
"Duplicate entry '' for key 3"
Im attaching the 2 files, checkout.php and confirm.php pages.
I did 2 types of tests:
In my Admin I created 2 voucher codes one being £80 and the second being £79
I then created an order consisting off:
Product Option £5
On the checkout page I was going to select the delivery cost of £7
This would then = £80 for the total order...
(so then I was going to test how the website tackles the grandtotal of £0 AND second test of grandtotal being £1 (If I had selected the voucher for £79).
However the logical error for all this is that the code you supplied is checking the grandtotal BEFORE i select my delivery option of £7 because it automatically bypasses the checkout and confirm pages and goes straight to success (then gives me that error "Duplicate entry '' for key 3")
I can see that if in the cart the grandtotal would be "currently" £73 (since i havent selected the delivery option on the checkout page) so the code assumes that the grandtotal is <=0.