Can’t personnalise the Meta Key for Video Post Type

When I’m giving a meta key to the video post type (_video_url for me), the plugin doesn’t use it in the AMP theme. I have to hardcode the meta key value in the single.php code :

		if ( get_post_format() === 'video' ) {
			$meta_key = better_amp_get_theme_mod( 'better-amp-featured-va-key' );

			if ( empty( $media_key ) ) {
				$meta_key = '_video_url';
			}

Your plugin is great, but I have to hardcode that every update… It would be nice to correct that bug. It’s just the better_amp_get_theme_mod( ‘better-amp-featured-va-key’ ); function doesn’t works and doesn’t return the right value ??