When you white label your domain Spiro takes care of the SSL Certificate to make sure the URL is secure, you just need to be sure to add the CAA Entry from the Custom Domain Section in Spiro and then verify.
To Access the CAA record that needs added to your account:
Visit your Custom Domains, click here
Scroll to the bottom of the added portals
Once you add the record to your DNS click Verify
NOTE: If you have white labeled multiple portals you will see this CAA entry for each portal however you only need to add the entry 1 time to your DNS for all portals.
Once verified depending on your domain the SSL certificate can take up to 4 hours (but be much less as well). Be sure to clear your cache to confirm you are viewing the latest version of the portal (or visit the page in a private window)