I had not configured the CNAME pointing the public address to the custom domain. Once I configured that, it worked.
Please check your HTTPs vs HTTP. Check which port you are using. If you are using HTTPS you will need to have that certificate also uploaded into AWS ACM most likely.
Further reading if HTTPS custom domain: https://lightsail.aws.amazon.com/ls/docs/en_us/articles/amazon-lightsail-enabling-distribution-custom-domains
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