For the Stromer Racktime-C4 Rear Rack (27.5" models) there is also a spring-loaded flap, as one knows from Biobikes. The somewhat unwieldy name is Racktime Adapter Clamp-it black, for the Light-it model.
There are different flap models that fit different carriers. The Stromer Racktime rack only fits with the Snap-it-1.0-Adapter and the corresponding Spring flap „compatible“. The Snap-it 2.0 (with the spring clamp Clamp-it 2.0) does not fit.
Attention: For electric models from around 2019 onwards, the center strut is missing on the Racktime racks, and thus the spring's locking point. This can be retrofitted relatively easily. When retrofitting, you need to ensure there is enough space between the retrofitted center strut and the fender so that the flap holder can be pushed through.
Another option would be to anchor the retaining spring in the mudguard using a washer and a pop rivet. (Source: stromerforum.ch | Calli)
