Why wasn't an order tagged as a preorder? (Essent Preorder Back in Stock app)

Orders are tagged when a customer buys through the Preorder button in your Online Store. Other cases:

• Shop app, POS, Inbox, Facebook & Instagram, TikTok: these channels don't use your storefront, so the app only catches the order if you tick the channel. Campaign → Content → Accept preorders in channels → tick the channel → Save. Needs the Starter plan or higher. Past orders need the tag added by hand.
• Third-party checkouts and marketplaces (for example GoKwik, Etsy or Amazon integrations) aren't supported.
• The product was still in stock when the order came in, for a "When out of stock" campaign. That's a normal order.
• The item was added to cart another way, for example a custom bundle button or an external link, not the Preorder button.

Set your own tag in the campaign → Content → Order tags. It applies to new orders only.

Full guide: Accept preorders from POS, Shop app and other sales channels.