The Robert Axle Project site has an adapter specifically for this. I just installed mine. It was super easy and works perfectly. 

https://robertaxleproject.com/product/trailer-hitch-adapter-for-rad-power-bikes/

Update! The LBS wasn’t able to mount the hitch but an adapter is available on the Robert Axle Project site. IIR it was about $37 and I received it in 3 days. It’s simple to install and works perfectly. All you do is remove the original axle nut, install the provided washer and adapter then install the hitch followed by another washer and the nylock nut. Took me about 5 minutes. Per the company this works on all RadPower bikes and pretty much any commercially available trailer hitch but it would email them first just to be sure.

1. Specialized Sequoia Elite road bike
2. Specialize Globe Hybrid
3. Specialized Rockhopper
4. Giant Alight Hybrid (guest bike)

And now a City 5 Plus with about 10 miles on it.

Looking to upgrade my road bike and considering a gravel bike so 7 sounds like a good number. 😁

Whelp, bike was delivered today! Took it to the LBS still in the box to build and give it a once over (watched the assembly video and read reviews, decided to let the pros do it right the first time). I gave them the hitch to see if they can make it work. If it can?t be axle mounted I?m going to McGyver a chain stay mount. This is a cargo trailer so no kids will ever be in it.

New here. Just pulled the trigger on the 5 Plus. I don?t have it yet but from research am anticipating a bit of a struggle attaching a trailer hitch to the axle. I have an older model Croozer trailer. I searched the forum but didn?t find much about cargo trailers before registering and posting. Does anybody have any experience with this? Much appreciated.