Does each website require a different API?

I ask because I put the same API key for two sites. I got the SSL certificate to work on one site. On the other site, however, I got a message saying “You already have an SSL certificate installed” when I was going through the installation. Now for that site, Really Simple SSL reads “SSL is activated on your site. You still have 7 tasks open.” but when I go to the site, I still get the red “Not Secure” warning from Chrome. Not sure what went wrong.