The API key I'm working with seems to have a referrer restriction, even though I only want it to be limited to Google Drive API. How can I fix this issue?

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You can try adding "https://www.googleapis.com" to the list of allowed referrers for the API key. This should limit the use of the API key to requests coming from the Google Drive API. To do this, go to the Google Cloud Console, select your project and then navigate to the Credentials page for your API key. Under the section "Application restrictions," select "HTTP referrers" and add "https://www.googleapis.com" to the list of allowed referrers. Save the changes and try using the API key again.