We just rolled out an update to our store from CE 1.7.x to 126.96.36.199. It is a really simple store with no addon extensions. The upgrade was smooth and everything seems to be working as expected except our coupon codes have stopped working properly. The coupon code is accepted by Magento, and a discount line item shows up in the totals if it is relevant, but the grand total is not updated in the cart or at checkout. We don't have anything custom that we are aware of that touches the cart total functionality, what else could cause this issue?
Solved! Go to Solution.
We fixed this by adding the following into /app/code/core/Mage/Sales/etc/config.xml sales/quote section.
<discount> <class>sales/order_invoice_total_discount</class> <after>subtotal</after> </discount>
This is a terrible solution, obviously, and I have no idea why it is needed. We will have to research it further to come up with a better solution than editing a core file!