How I can use a specific variation google font?

Hi, I need to use Open Sans Normal 400 fot the paragrahs and Extra-Bold 800 for the titles, but in the stilyng i only can specify a simple Open Sans option.

I have added the following on function.php but did not work

add_filter( ‘avf_google_heading_font’, ‘avia_add_heading_font’);
function avia_add_heading_font($fonts)
{
$fonts[‘Open+Sans:800’] = ‘Open+Sans:800’;
return $fonts;
}

add_filter( ‘avf_google_content_font’, ‘avia_add_content_font’);
function avia_add_content_font($fonts)
{
$fonts[‘Open+Sans:400’] = ‘Open+Sans:400’;
return $fonts;
}