Every webhook starts with specifying the table, the operation to trigger your action (in this case "when data modifies") then specifying what fields to look for (in this case your date field) and then what condition to meet after the change (in your case, that date has a value) BEFORE specifying what you want to do with it. In this case, if you want to integrate with a third party service, you should be able to mention what your target is, and what message you want to send. You don't need an API to pull the data changed. Is that helpful?
