Adding custom fonts

Hi

I have followed all the instructions to add local fonts and I have successfully added one new font which I can select via the customiser. However I can't add a second font - it's not appearing in the customiser list. Below is the filter I am using. Do I have the syntax wrong? Hope you can help.

Thanks,
Helen

add_filter( 'generate_typography_default_fonts', 'tu_add_local_fonts' );
function tu_add_local_fonts( $fonts ) {
$fonts[] = 'proxima_novaextrabold, proxima_novaregular';
return $fonts;
}