Custom font adding hook for WP Tabs Pro.

add_filter( 'wptabspro_field_typography_customwebfonts', 'wptabspro_field_typography_customwebfonts_modified' );
if( ! function_exists('wptabspro_field_typography_customwebfonts_modified')) {
    function wptabspro_field_typography_customwebfonts_modified() {
        // your custom fonts 
        $custom_fonts = array(
            'use your desired font name',
            'Manrope',
        );
        return $custom_fonts;
    }
}