How to execute sync/copy or sync/sync with --dry-run option via POST request to the API

Thanks @Ole, that seems to work if I submit my JSON in the body as raw encoded JSON. But to my surprise there is no content/JSON delivered back to me. I get a 200 response, but it does not have any content other than {} while the rcd spits out lots of lines of what it actually checks. I am puzzled, what is the use of that option if I do not get a result back?

BTW, I fire up the remote control daemon with:

rclone rcd /home/pi/data --rc-user=bot --rc-pass=secret --rc-addr= --rc-allow-origin= --rc-web-gui-no-open-browser --log-level=DEBUG