curl -k -u admin http://netxms:8080/webapi/alarms -X GET -d '{"alarm":"outstanding"}'

It is returning all alarms regardless of whether they are NORMAL, WARNING, CRITICAL but its a start.

I see:
{"description":"NetXMS web service API version 3.7.130","version":"3.7.130","build":"3.7-130-gc909bacd30"}

However if I try to use the curl command I got from the netxms page here: https://wiki.netxms.org/wiki/Web_service_API
nothing is returned.

curl -X POST --data '{"login":"admin","password":"xxxx"}' "http://netxms:8080/webapi"

Have you got any examples of correct command?

I am hoping to run a command that will return devices to get their status, ie: UP or DOWN