PHP do_shortcode problem

Hello, I am having trouble getting this code fully rendered.

if(!function_exists('_admin_testing_embedded_video')) {
	function _admin_testing_embedded_video($postid) {
		$post_type = get_post_meta( $postid, IT_META_POST_TYPE, $single = true );
		if($post_type=='article') return false;
		$stream1 = get_post_meta($postid, IT_META_STREAM_1, $single = true);
		if(!empty($stream1)) {
		$out .= '<div class="stream-container">';
				$out .= do_shortcode('[nextpage title="Stream 1"]<iframe src=' . $stream1 . ' width="100%" height="440px" frameborder="0" scrolling="no" style="margin-bottom:15px;"></iframe>[/nextpage]');
		$out .= '</div>';
		}
		return $out;
	}
}

I also tried using apply_filters(‘the_content’) but couldn’t get it to work. It shows page numbers, they’re clickable but it doesn’t output the content nomatter what I input.. within the shortcode.

The plugin works normally on a wordpress test page, however I need it to work via PHP.

Any ideas or solutions, or is the plugin incompatible to function via PHP outputs?

Regards,
Fayche.

https://www.ads-software.com/plugins/advanced-content-pagination/