400: Missing font family
The requested font families are not available.
Requested: '.urlencode($main_font).' (style: normal, weight: 400),'.urlencode($main_font).' (style: normal, weight: 800),'.urlencode($main_font).' (style: italic, weight: 400),'.urlencode($main_font).' (style: italic, weight: 800)
For reference, see the Google Fonts API documentation.