Redirection to my site after paypal payment

I'm currently testing the paypal addon with Paypal Sandbox environment. I have created a "thank you for your payment" page to be displayed after payment and entered this URL within the Paypal settings. However, when I finalize a payment within the Sandbox environment, I'm not redirected to my site after the payment. For some reason the URL is inluding port 443 which renders in an error. It looks like this: http://mysite.com:443/encrypted url...

If I manually remove the :443, I'm redirected to the page I have created. I'm using SSL on my site.

The error I'm facing is:

400 Bad Request
The plain HTTP request was sent to HTTPS port

Have I done something wrong regarding the necessary settings?

I have now tried with the "real thing" but the problem remains. Paypal is not adding "https://" to the redirection address with following 400 Bad Request error. Any solutions?

I've created a single page for the cancel message and put the url in the Paypal feed setting:

https://www.domain.com/predefined_page