Then, take the exported cert to the target server and install it, again, as per Jack's instructions below. After this, you can then define your SSL binding within IIS.

Moving an SSL certificate to a new server isn't always straight forward. Moving one from Godaddy to a new Windows Server proved down right frustrating.

Let's Encrypt is about to stop sending emails for expiring certificates, so now's the time to check your renewals are working.

After importing the SSL certificates (without checking the allow keys to be exportable option), i get errors when binding the certs in IIS.