[kevindong]

It's literally just:

1. Here's a URL (custom to each user/applet). You can either GET or POST to it. No auth/headers required (the URL includes a token).

2. You can optionally submit a JSON in the format of {"value1": ..., "value2": ..., "value3": ...} and set up the applet to set those values as the notification title, body, link, or image.

Rather unfortunately, you can only specify three values in the JSON so you can only ever have three of those four properties filled in for a single notification. But you can set up multiple receiving URLs/applets such that you can send the first notification containing three of those properties and then a second notification containing the last property.

[m-p-3]

I hope we'll see more than three values as a possibility with IFTTT Pro.