Water only comes out of the first nozzles/drippers, what could be the cause?

If water only comes out properly from the first consumers, this may be because the capacity of the water connection is insufficient or because it is dirty. The GARDENA basic units have a dirt strainer, which should be cleaned as required. You can check whether the watering system is correctly designed using the watering leaflet "Micro-Drip System 2: Assembling your Micro-Drip system".