Hi,
You don't need that.
HikaShop sends its IPN URL to PayPal for each payment request. So PayPal already knows the URL to notify the website for each payment, even if the payment requests come from different websites.
That IPN setting is sueful for when the website doesn't send the IPN URL to PayPal.
I would be more concerned about the order_id overlapping on both websites:
www.hikashop.com/support/documentation/i...l-error.html#already
If you don't confiugre your PayPal merchant account properly, you're likely to have that error "This invoice has already been paid. For more information, please contact the merchant"
The cancel and return URL settings are to let know PayPal were to redirect the customer after the payment if it succeed or fails. It's not linked to the IPN or the order status changing to "confirmed".