While the fulfillment status of the order isn't a requirement for how orders sync to Vend, if you want your Shopify orders not to show in Vend before being fulfilled, as a workaround you can archive unfulfilled orders in Shopify and then get new orders from Shopify to Vend as archived orders will not sync through.
- Shopify Integration
- Click Setup>Add-ons>Shopify
- Untick "Update Vend" option.
- Select the unfulfilled orders in Shopify.
- Click Actions>Archive Orders
- In Vend, Click Get Shopify Orders > Get New Shopify Orders.
- Wait till all the fulfilled orders have synced in Sales Ledger.
- Back in Shopify, select the archived orders.
- Click Actions>Unarchive Orders.