Adapt Shipstation implementation for Shopify in order to make sure its compatible with Post Purchase 1 Click Upsells and the OneClickUpsell OCU app for Shopify.
The latest Shopify Fulfillment API allows for fulfillment holds so post-purchase offers products can be smoothly added to orders: https://shopify.dev/changelog/post-purchase-fulfillment-holds
Currently, Shipstation orders are showing with 0 quantity when auto-fulfilled until the upsell funnel is complete (1 hour) or TY Page is reached.
Having this feature would allow Shopify store owners to use the apps together and increase Average Order Value seamlessly. Provide merchants with a significant increase if profitability that is lost without post-purchase upsells.