1) Create an "Incoming webhook" integration in Slack
You can do this in "Team > Apps and Integrations > Manage > Custom Integrations > Incoming WebHooks"
This will give you WebHook URL you will need in NetXMS.
2) In NetXMS, go to "Server Configuration"
Filter for "sms". You should find "SMSDriver" and "SMSDrvConfig" server configuration variables.
3) Configure "SMSDriver" with the path to the slack driver
If running from Debian packages, the path will be "/usr/lib/x86_64-linux-gnu/netxms/smsdrv/slack.sms" or similiar.
If you compiled manually, the path will be as per your ./configure settings. (example "/usr/local/lib/libnxsms_slack.so")
4) Configure "SMSDrvConfig" with Slack configuration
This configuration needs to provide "username" and "url"
"username" is optional, if configured, NetXMS will post with this username into your Slack. If not configured, configuration from the WebHook settings is used.
"url" is the URL of your WebHook.
Final configuration string should look like this: "username=user;url=http://url.slack.com"
5) Create an Action to send Slack messages
"Configuration > Action Configuration > New action...", type "Send SMS to mobile phone", "Phone number" is the Slack #channel or @user where the message should be delivered.
"Message text" is your NetXMS message, configured the same way as other actions.
6) Modify EPP to use your new action
You should now see Slack messages posted to your configured destination, when the EPP action takes place.
Set debug level to 4 ("debug 4" into Server Console).
You can now look for interesting debug messages in the logs:
tail -f /var/log/netxmsd | egrep "[Ss]lack|sms|SMS"