Hi Cor,
The redirection URL was missing from the options: http://i.imgur.com/68PEMkO.png
I’m not sure why or what it was, but I added this value there:
?s={phrase}
I think this is the correct one. If that was not it, then you can try this one as well:
?s={phrase}&post_type=al_product
Both should work, but I don’t know which one was used.