1. Edit job and set empty schedule.
You must look at the url and remember id!

2. You should open tab "Settings" ,  open "jobs" , click "Generate new key" and click "Save".

You should open tab "Settings" ,  open "jobs" (again!)  and copy key only 

3. Modify  this url .  


{site.com}  is your website url

{job_id}  - you get this ID at step #1

{key}  - you get this key  at step #3

if you use HTTPS,  replace http with https too!

Final result must looks like 


4. Test it, open this url in browser , you should get message

Scheduled job #XXX. Result: .....

You can use this url in external scripts  OR  call it (for example) via curl/wget