Chrome Extension InApp Payments - TOKEN_MISSING_ERROR

https://console.developers.google.com/apis/credentials

Create credentials, select OAuth client ID, Application type as Chrome App.

In your manifest.json,

"oauth2": {
    "client_id": "??????.apps.googleusercontent.com",
    "scopes": [
        "https://www.googleapis.com/auth/chromewebstore.readonly"
    ]
},