The reason your shortcode is still showing the full JSON is that extracting a specific value using the keys="" parameter is not available in the free version of WPGetAPI. This feature—allowing you to display only data.total_auctions like 103—is only available in the Pro (paid) version.
In the free version, the plugin will always output the full JSON response. To achieve the result you want, you would need to upgrade to WPGetAPI Pro.
If you upgrade, make sure the key path (data.total_auctions) matches your API response so the plugin can fetch it correctly.
For reference, see the official documentation on retrieving nested data: