ERR_NAME_NOT_RESOLVED while trying to set up AWS to point to Heroku

When I head over to example.com in a web browser, I get ERR_NAME_NOT_RESOLVED.

$ host example.com
Host example.com not found: 3(NXDOMAIN)
$ host www.example.com
Host www.example.com not found: 3(NXDOMAIN)

Here's what I've done.

I've followed the instructions on Heroku's webpage. I'm trying to point example.com -> example.herokuapp.com.

Heroku seems to be set up properly.

$ heroku domains
=== example Domain Names
example.herokuapp.com
example.com
www.example.com

In S53, there's an A-level ALIAS for s3-website-us-west-2.amazonaws.com., the S3 Bucket. The S3 bucket, named example.com, has enabled Properties > Static Website Hosting > Redirect all requests to another host name > www.example.com . So A-level should redirect to www.example.com.

In S53, www.example.com has a CNAME -> example.herokuapp.com. So that should work, too.

The four nameservers listed as NS for example.com are:

ns-618.awsdns-13.net.
ns-1481.awsdns-57.org.
ns-1908.awsdns-46.co.uk.
ns-239.awsdns-29.com.

When I head over to Registered Domains, the nameservers there for the domain are the exact same.

At this point, I have no idea where to start troubleshooting. Have I missed something glaringly obvious? How can I try to figure out where the problem is?