Relative position seems incorrect

First, thanks for this super handy addon to i3!

I have this in my config file :

bindsym $mod+Ctrl+dollar exec --no-startup-id "i3-scratchpad -acc -d800x600 -mb -t alacritty -e cointop"

That should show the scratchpad in the center, with an animation from the bottom.

Instead it shows it on the top left of the screen, with the center of the scratchpad at 0,0 :

Have you ever encountrered this issue ?