How to call en external web API once a tag is applied to contact

I would like to call an external web API on applying the Tag to contact. I tried to achieve this by creating action sets and setting an action to “Send Http post to another server”. I set some criteria to it. But when apply required Tag to contact to trigger http post it does not work. Please let me know if there is any way to call external web API as soon as an Tag is applied to Contact.