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 ngrok to 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.
After you download your HTML verification file, copy it into Appmixer engine.
docker cp google52658022a92d779c.html appmixer-401_engine_1:/usr/src/appmixer/gridd/public
After then, click the 'Verify' button and that's it. You don't need to restart the Appmixer engine.
Now, you can go back to developer console and add the ngrok domain once more.
But this time, because it's already verified, it will appear in the list of your domains.