This could happen for many reasons.

First check if your certificate was successfully issued from ASS Certificate Manager. In the table (last screenshot in step 2), the status column should be “Issued” and In use? column should be “Yes”.

Make sure you associated the certificate with your website in your website’s distribution settings (in Step 3) and that the “Behaviors” tab has your HTTPS behavior listed (done in step 4).

AWS Cloudfront can take hours to reflect these changes depending on the region and their availability.

If you are sure you have everything configured correctly (make sure there are no typos!) submit a ticket to AWS support who can pinpoint the problem for you.