There are two options here.
- the monday dev center offers builtin triggers. One of those is a “column change” trigger.
- you can create a custom trigger (with a subscribe and unsubscribe endpoint) and create a webhook through the API in the subscribe event. Don’t forget to delete the webhook in the unsubscribe event. You webhook endpoint can analyze the payload of the webhook and (in the app) you decide to post to the subscription URL, which will trigger monday to post to your action endpoint from your custom action.