Your developer HAPIkey is used when managing settings related to your HubSpot apps through the API. This would include managing subscriptions for the Webhooks API, creating or updating event types for the Timeline API, or managing the settings for the Ecommerce Bridge.
Note: Developer HAPIkeys can only be used for managing those settings. Developer HAPIkeys cannot be used for accessing the data APIs, such as the Contacts API. You must use the hapikey from a specific portal to access the data for that portal. If you are looking to test the data APIs, you can create a test portal, and get the hapikey from that test portal.
Your developer HAPIkey can be found inside your HubSpot developer account, by clicking the Get HAPIkey button at the top of the Applications dashboard.
This will open a window that contains the developer HAPIkey and your user ID.
If your developer HAPIkey is compromised, you can deactivate the current key and generate a new one using the Regenerate key button at the bottom of the popup window.