I built a Transport Drone Fuel Refinery and connected it to the Fuel Depot. The depot filled up with fuel (a pink-colored drop).
I placed several vehicles there and connected it by road to a Request Depot and a Supply Depot.

The Supply Depot provides copper plates, and the Request Depot requests them. When I placed vehicles in the Request Depot, trucks started driving from the Fuel Depot to the Request Depot with fuel.

But for some reason, the Request Depot is requesting petroleum gas and doesn’t accept drone fuel.
As a result, the drones from the Request Depot don’t go anywhere, and the drones from the Fuel Depot keep driving back and forth endlessly.