Require help installing Instep Bike Trailer to my ebike

[indca]

Hello guys;
I am trying to install the coupler in my ebike BPM F15-RS;
I have tttached pictures for your review: as I just bought an instep two kids bike trailer but the coupler that attaches to the rear wheel of my ebike bolt is bit small; my bolt it seems is 19 mm in size; do you guys have advice or reccomendation to get a correct size coupler? Where can I buy that can work with my ebike?
Link to the item will be appreciated; thanks.

 

[WattsUpDude]

There’s a few different standards for trailer attachments. See if this one works for you.