You can add a custom stream to be pushed once a hotspot is clicked. This is used for API calls, i.e., custom data can be passed from the API event field in the hotspot editor, allowing you to listen for and collect specific data on the host page.
Additionally, when enabling the 'API Timeline' we are able to add custom data in specific cue points throughout the video. See screenshot: http://prntscr.com/omvbr3
This is unlike the aforementioned custom data field, where the custom string is linked only to the 'Click' events.
Cue points are custom timed events that can be placed at any point in a given node using the API timeline in the node editor of the Rapt KMS module. These events accept custom data, which is passed through the event as customData.