In order to use Google API Webhooks you have to verify your domain ownership. More about domain verification can be found in here. When Appmixer is running on your servers, you can use CNAME records to verify your domain ownership, but if you want to use components that use Google API Webhooks (appmixer.google.drive.NewFile for example) in an Appmixer instance running on your localhost (typical for testing the trial or when developing new components) you need something else. When running Appmixer on localhost, you usually use tools like ngrokto create public tunnel to the Appmixer API. In order to verify ngrok domain ownership you can use the HTML file method .
First, open Google developers console and your Appmixer project and follow instructions in the next picture.
Then copy&paste your ngrok URL.
Then you have to verify domain ownership.
Click 'Take me there' and then 'Add a property'.
Then download the HTML verification file.
Download HTML verification file
After you download your HTML verification file, copy it into Appmixer engine.