Trying to add a Google font

Hi,
I tryied to add the Comfortaa google font with greek laguage extention.
1. I installed the child theme

2. I added in functions.php of the child theme the following:

add_filter( ‘avf_google_heading_font’, ‘avia_add_heading_font’);
function avia_add_heading_font($fonts)
{
$fonts[‘Comfortaa’] = ‘Comfortaa:300,300italic,400,400italic,700,700italic&:greek’;
return $fonts;
}

add_filter( ‘avf_google_content_font’, ‘avia_add_content_font’);
function avia_add_content_font($fonts)
{

$fonts[‘Comfortaa’] = ‘Comfortaa:300,300italic,400,400italic,700,700italic:greek’;
return $fonts;
}

The problem I have is at bold (emphasized) text, the “Comfortaa” font is ignored.
Thank you in advance for your help.