Not an official Shopify app
Shopify packing slip API
Map the order JSON you already have. POST it from a Print Action or a fulfillment worker. Slipmill is not listed in the Shopify App Store.
Shopify merchants who want a branded packing slip usually hit the theme editor or an app that owns the HTML. Slipmill is a render mill. Your worker reads the order, maps fields, and POSTs.
We are not an official Shopify app. There is no OAuth dance and no embedded admin. If you have a fulfillment service or a custom app, you already have the JSON.
The preview tool can accept a Shopify-shaped paste and map it client-side so you can see the mill fields before you write production code.
Questions
No. We are not listed in the Shopify App Store. Your worker or Print Action maps order JSON and POSTs it.
No. Send packing-slip JSON. Two locked templates we own. The mill returns US Letter application/pdf.
x-sm-key. POST /v1/render. One request is one PDF.