What do I need for warehouse deliveries to work?

Start with the boring checklist. You need a warehouse business with usable storage, a vehicle assigned to the warehouse, an eligible driver, a headquarters workstation for the Logistics Manager, and a destination route with a sensible stock target.

Then check the flow in order: did the goods arrive, is the item allowed at the destination, is there free shelf space, and does the route have enough capacity? Fix the first broken link instead of changing every setting at once.

Source notes: the official Steam page and the warehouse and delivery guide.