Redirect after a succesful paypal donation

[AnisotropicDefixation]

I am talking about the intended redirect to the "?module=donate&action=complete page.

It seems to not work no matter what. Adding the page to paypal's automatic redirection does nothing either.

After a donation is made, you're just sent to ?module=main, there isn't any attempt to reach the intended page.

I've played around for a bit and I think the issue might be coming from this bit in preprocess.php:

if ($params->get('merchant_return_link')

It seems like merchant_return_link isn't being sent by paypal during the IPN confirmation, although even removing that check doesn't help either.