Bad link generated upon Prosite upgrade

In using the Stripe gateway and upgrading a Prosite level from free trial to paid, it shows the following after the payment is successful on a live test:

"Your subscription was successful! You should be receiving an email receipt shortly.

Thank you for your purchase! Your payment was received!

Visit your newly upgraded site »"

Cool, it works... However, the link on "Visit your newly upgraded site »" is a broken link and points to for example:

https://multisite.com/premium/testsite1.multisite.comwp-admin/

As you can see, that link is all messed up, it sticks a malformed version of the admin url and places it behind the address of the 'checkout' page.

This is a no-no as it's the obvious link that points them back to their account to see their upgrades. Does this have anything to do with an https backend? Any suggestions?

Thanks!