I am currently using Amai PreOrder Manager + Notify, and discovered that it does not work for pre-orders that have paid with Express Payment Methods. I have items on PreOrder with inventory limits, and I ran a report within the PreOrder Ap and some of my orders were missing. When I enquired, Amai told me it is because those orders were paid with Express Payment and it is a limiation of Shopify. This has resulted in going over inventory limits and having to cancel orders.
Has anyone else experienced this?