Sylius version affected: 1.12, 1.13

Description
The rule "total price of items from taxon" so the checker Sylius\Component\Core\Promotion\Checker\Rule\TotalOfItemsFromTaxonRuleChecker wrongly checks whether the promotion is eligible or not. It sums up the order items total but if the coupon is already applied and decreased items total then the rule starts denying the coupon and you cannot go to the checkout.

Steps to reproduce
Let's have the cart promotion configured as follows:

And let's say the product variant in the taxon costs €20.38.

Now let's add 3 of them to the cart and apply this coupon code. All works as expected:

But now if I try to go to the checkout, I can't. It happens because coupon validation is triggered for a second time and the rule is not met anymore.

Possible Solution

• Consider the order of order processors.
• Calculate the sum of order items based on variant price rather than the order item total.