I was working on a custom function for a client to create purchase orders automatically. Everything worked fine except the product details. When you look at the JSON for a purchase order, it uses "product" for the line items. However, if you try and do the same thing when creating a purchase order, it seems to completely ignore the "product" property. Fortunately Ruben came through with a video that explains how to solve this. You have to use "Product Details" as the key instead of "product".
Here's a code snippet: