SSL Installation on Lightsail

I have ran a small LAMP application for years on Lightsail and now need SSL to embed content elsewhere.

The app is resolving into a subdomain of my primary vanity domain I only use for this app.

I've created a SSL Certificate in my registrar (namecheap) and installed it into an AWS Distribution. The certificate is showing "Valid, In Use" but the custom domain is saying "Domain not registered to account".

Looking at my domain in AWS, I have an A record with "www.mydomain.com" pointing to the cloudfront domain. I have a CNAME record pointing to my static IP.

Looking at my registrar, I have an A record pointing to my subdomain (sub.mydomain.com).

The app continues to work in HTTP but not HTTPS, so my users are not impacted. I have no clue what is my next step. Thanks in advance for any assistance you can offer