Last to Cart is somewhat similar to Last Click in that one of the last steps a customer takes in the conversion path will determine which partner receives all the credit and payout for the conversion. Instead of the last click event a customer generates determining this, though, the last time a customer adds an item to their cart will determine the winning partner.
With the Last to Cart policy, the partner that drove the customer to add the final item to their cart before checking out, will almost always receive 100% of the credit, and usually all of the payout for the conversion. However, receiving full credit may be dependent on your participation bonus setup.
Let's check up on The Roadrunner one last time. They're confused as to why the conversion paths are the same, and want to try using the Last to Cart policy since they're dealing with partners upset with the change to the First Click credit policy. After talking with their CSM again, The Roadrunner decides they care most about when the customer adds items to their cart, and their CSM initiates the change to the Last to Cart policy.
Funny enough, The Roadrunner's conversion path still does not change. Customers add paint brushes after clicking through the home improvement blog's banner ad, add tarps after clicking through the sponsored search result, and check out after clicking through the sponsored Instagram post. With this latest switch, the partner that owns the sponsored search result is now winning all conversions since they drive customers to add the final item (the tarp) to their cart before checking out.
How do I request this credit policy?
Reach out to your CSM (or contact support) to discuss enabling the Last to Cart credit policy. You'll want to share why you want to use this policy and if all your partners will be on Last to Cart (and if not, which policy should take priority in a journey if more than one policy is present).