Codes and automatic discounts
If an entered code doesn't apply, the cart shows the reason. About discounts explains how coupons and automatic discounts differ.
Coupons with Show in cart turned on can be suggested to shoppers before they enter a code. See Discounts, Gift Cards and Store Credit at checkout.
After too many codes that don't work, the shopper must wait up to 15 minutes before trying another: the 15 minutes count from the first code that didn't work. Codes that work don't count toward this.
Free gifts
With Add automatically, the gift goes into the cart as soon as the order qualifies and is removed if the order stops qualifying. With Offer to claim, the shopper sees the unlocked gift and adds it to the cart themselves. How an offered gift looks depends on your theme.
When the total changes before payment
If the total changes after the shopper reviewed it, for example because a discount stopped applying or its saving changed, the order isn't placed. Checkout shows the new total for the shopper to confirm before paying.
A payment retry keeps the order's prices while its checkout is still open. Once the checkout has expired unpaid, a new checkout prices the cart again with the discounts that apply then.
After the order
If you edit an order that used a Buy X Get Y or bundle offer, the saving stays on the items it was given to and doesn't move to other items. Reducing an item's quantity reduces its share of the saving in proportion; removing the item removes its share. See Edit an order.