The default gelf port is 12201 and you only need /gelf so try:
curl -H "Content-Type: application/json" -X POST -d '{"host":"mylocal box","message":"cimbombom","priority":"realy low"}' http://10.10.20.61:12201/gelf
There are some command tips here including a sample curl to gelf.
On a side note - in your post the quotes are “fancy” some are " instead of " so they don’t copy/paste well for commands. Use the forum tool </> to format commands nicely as above. 
EDIT: While poking around on a similar question I came across this quote from @jochen:
" Also be reminded that the regular expression has to match *the complete field content* if the field hasn’t been tokenized/analyzed."
So you could either create a custom mapping to have the entire field analyzed or you can split up the field to its constituent parts in an extractor or pipeline so that you can query relevant information.
As such it seems that “zoom” doesn’t appear in the $message.message field, otherwise it would be found (Message is an analyzed field)