Hello @EllieB,

Welcome to the Klaviyo Community!

I’m unsure of any specific pre-order/backorder Shopify apps that would integration with Klaviyo, however, there are a number of third-party ones that do! You can find a list of a number of third-party integrations that have developed their own connection to Klaviyo from our Partner Integration Directory.

I would love to learn more about what specific Shopify apps other members are using for pre-orders with Klaviyo too!

David