The status of this certificate request is "Failed". One or more domain names have failed validation due to a Certificate Authority Authentication (CAA) error.
After googling around, I found this note:
One or more domain names have failed validation due to a Certification Authority Authentication (CAA) error, check your CAA DNS records..
After going back to my domain in the Vercel dashboard, I found this record:
CAA 0 issue "letsencrypt.org"
Since there is no CAA Record allowing amazon to issue certificates, the request fails.
AWS provides documentation on how to configure a CAA record to allow ACM to generate certs. We need to add an extra record in Vercel:
CAA 0 issue "amazon.com"
Request a new ACM cert and this time it succeeds!