Is there an app that combines orders?

[jasonzeyu]

Hey guys, with my current store, I sell a main product and then a separate product that is an add-on to the first product. A customer would purchase product A (paid shipping), creating an order, then comes back 5 minutes later and purchase product B (no shipping because it is an add on). Now because product A hasn't been fulfilled, it is ideal for the second order to automatically be merged into the first order and shipped together via the chosen shipping method. Currently, our backend is having a hard time finding and combining these orders because the shipping method is labeled differently.

No, we cannot ship them individually as they are too cheap.

Yes, we already have bundles and upsells however this is for customers that return from email marketing or retargeting.

I want to ask whats the most efficient way to do this or is there an app for something like this? Thanks