Dog trailers come with the same fundamental mechanism of attaching a trailer or second unit to your vehicle. So, you’ll need to install the universal hitch right onto your bike’s axle.
If your bike comes with a quick-release axle you’ll have to remove the skewer and insert this through the hitch opening. Push the skewer into the bike axle and secure it well. Push the latch securely. Don’t worry about the positioning of the hitch as it will naturally correct itself.
If your bicycle comes with bolted axes you need to remove the axle bolt. Put the dog trailer bike hitch onto it and secure the bolt. If your bike has an internal gear right within the wheel hub, then you need a hitch adapter.