What does 'Invalid argument (callbackUrlScheme): must be a valid URL scheme' mean?

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This error message usually means that the value you entered for the "callbackUrlScheme" parameter is not formatted correctly or doesn't match the expected format. "callbackUrlScheme" refers to the URL scheme that will be used by the API to send callback notifications to your application. To resolve the issue, you should make sure that the value you entered is a valid URL scheme and is correctly formatted.