order link doesn't work, untill I add "add=1"

[yolknet]

After updating a 4 year old prestashop version the order button doesn't work any longer on this page: http://www.yn2.nl/onstejater/index.php?id_category=5&controller=category&p=2

I found out the button works when I change this line

http://www.vierbinden.nl/onstejater/index.php?controller=cart?add&id_product=63&token=75928323bb2ad358344bbaf4d4f79d21

to this line (change "add" to "add=1")

http://www.vierbinden.nl/onstejater/index.php?controller=cart?add=1&id_product=63&token=75928323bb2ad358344bbaf4d4f79d21

How can I repair the order link?

 

[rocky]

It seems your theme is not compatible with PrestaShop v1.6, only v1.5. You'd be better off creating a new one based on the default PrestaShop v1.6 theme.

 

But if you're unable to do that, you can try to hack your current theme into working. You'd have to edit themes/onstjater/product-list.tpl, search for the code that adds ?add to the URL and change it to ?add=1