Racks for 20" folding bikes/ebikes need to be frame specific.
Most racks for typical 26"+ almost never work since they hug too close towards the seatpost.
Look at 20" bikes that include racks from the factory, you want to get something like those.
I suggest against mailorder as it will be a hit and miss game.
Your LBS will cooperate in finding a compatible rack, they have branded racks like Axiom, Filzer, Thule.
Used shops/dealers/flippers may also have something lying around for donor.
20" folding bikes aren't new, many came with racks.
