Certificate in Certificate Manager is stuck in Pending Validation state from 2 days

I think in this case the most probable cause for your problem es from the troubleshooting section the point number 1. Is your route53 DNS zone publicly available? double check that trying to resolve the CNAME record from outside using online tools, or commands like dig or nslookup.

Best,

The issue you're experiencing with AWS Certificate Manager (ACM) is not uncommon. Even though you've entered the correct CNAME records in Route 53, there are several reasons why your certificate might still be stuck in the "Pending Validation" state:

1. Time delay: Although you've waited for 2 days, sometimes the validation process can take up to 72 hours (3 days). It's possible that you may need to wait a bit longer for the validation to complete.

2. DNS propagation: While you've added the CNAME records correctly, it's possible that the DNS changes haven't fully propagated across all DNS servers. This can cause a delay in the validation process.

3. Certificate usage: Ensure that the certificate is actually in use by an AWS service. ACM only automatically validates and renews certificates that are actively being used.

4. Multiple domains: If your certificate covers multiple domain names, make sure you've added the correct CNAME records for all of them. The certificate won't be issued until all domains are validated.

5. CAA records: Check if there are any Certification Authority Authorization (CAA) records that might be blocking the certificate issuance. These records can prevent ACM from issuing the certificate even if the DNS validation appears correct.

6. Terraform state: Since you're using Terraform for infrastructure management, ensure that your Terraform state is consistent and that there are no conflicts between your Terraform configuration and the actual AWS resources.

To troubleshoot further:

1. Verify that the CNAME records are publicly resolvable using DNS lookup tools like 'dig' or 'nslookup'.

2. Double-check that there are no typos in the CNAME records and that they exactly match what ACM provides.

3. If possible, try requesting a new certificate manually through the AWS console to see if the issue persists outside of Terraform.

4. Check if there are any error messages or additional details in the ACM console that might provide more insight into the validation issue.

If the problem continues after checking these points and waiting for the full 72-hour period, you may need to contact AWS support for further assistance, as there could be an underlying issue with the ACM service or your specific account.

Sources
Certificate Manger is pending validation after 48 hours | AWS re:Post
Certificate Status still pending validation | AWS re:Post
Certificate Renewal Still Pending After Updating DNS Records | AWS re:Post