PPL strings don't work

Hi!

I migrated my website from to another server, and now all my PPL strings don’t work anymore.

I use for example in my template file:
<?echo ppl_link_page(4); /* Contact */?>

But unfortunately on my new server nothing appears on the screen.

This is what’s in my functions.php:

function ppl_ID($id){
	$translated_id = pll_get_post($id);
	if($translated_id!=0){
		return $translated_id;
	}else{
		return $id;
	}
}

function ppl_get_page($id){
	return get_page(ppl_ID($id));
}

function ppl_link_page($id){
	$id = ppl_ID($id);
	return '<a href="'.get_permalink($id).'">'.get_page($id)->post_title.'</a>';
}

Hope someone can help me out, thanks!

https://www.ads-software.com/extend/plugins/polylang/