Zündapp 3-Wheel Delivery Vehicles, 1926-1938
In 1926, the first Zündapp motorized luggage tricycle came out in four versions. Powered by a 249cc two-stroke engine, they had full suspension and carried 150 to 200kg. 
Others followed, and in 1931 a three-wheeler appeared with a 200cc Zündapp engine. This was designed by Fideles Böhler, previously of Hanomag, and had a 500kg payload.
In May 1938 delivery van construction was discontinued.
Notes: 1. AOM states that it's an NK engine (Zweitakt-NK-Motor). This is possibly a misprint.
Source: Axel Oskar Mathieu Archive