That clears it up! I was looking at the picture of the mid drive bike. You have the hub motor version, What you're looking at is the motor cable. On most bikes, there's a disconnect on the cable to facilitate removal of the rear wheel for tire changes. Look in your owners manual to see if they describe it. It's not something you want to disconnect unless circumstances like a flat tire warrant it.
Whether you can fit your trailer adapter depends on whether the end of the motor connector will fit thru the 12mm axle nut. On some bikes it will. On others, it's too big. This is probably something to ask your bike shop if you bought the bike at one. If the cable end prevents the nut from coming off, you're out of luck.
In either case, the hole in your adapter is probably only 10mm and would need to be opened up to allow even the smaller cable end to fit thru.
This is a pic of my hitch adapter, one of my motor cables, and a 12mm axle nut. In this case the male connector goes right thru the nut, but the other end would not, and some bike makers use bigger connectors that won't pass thru.
I use my hitch adapter on a mid drive bike so I don't have to worry about it, but if necessary I would enlarge the hole to fit my hubmotor bike.
