Unable to Verify Custom Domain in Azure App Registration Despite Correct DNS and Validation File

I am trying to verify a custom domain for Publisher Verification in Azure App Registration, but the verification continues to fail even though all validation requirements appear to be correctly configured.

Domain: avistais.com

Validation File URL: https://avistais.com/.well-known/microsoft-identity-association.json

The file is publicly accessible and returns the following:

{
  "associatedApplications": [
    {
      "applicationId": "0d5471d1-50e2-426a-afdb-4b1f4c87a589"
    }
  ]
}

HTTP Response:

• Status: 200 OK
• Content-Type: application/json
• HTTPS enabled with valid SSL certificate

Response headers:

HTTP/1.1 200 OK
Content-Type: application/json; charset=utf-8
Cache-Control: no-store, no-cache, must-revalidate, max-age=0

Additional checks performed:

• The JSON file is accessible from browsers and curl.
• No AAAA (IPv6) records are configured for the domain.
• The hosting provider has confirmed the DNS records are correctly configured.
• The domain is verified in Microsoft Partner Center.

Despite this, Azure App Registration continues to fail domain verification.

Has anyone encountered a similar issue where the validation file is accessible and correctly configured, but Azure is still unable to verify the domain? Are there any backend validation logs, known issues, or additional checks that can be performed?

Any guidance would be appreciated. Cache-Control: no-store, no-cache, must-revalidate, max-age=0

Additional checks performed:

• The JSON file is accessible from browsers and curl.
• No AAAA (IPv6) records are configured for the domain.
• The hosting provider has confirmed the DNS records are correctly configured.
• The domain is verified in Microsoft Partner Center.
• Microsoft support has indicated that the issue may be related to Azure App Registration Publisher Verification / MPN domain validation and advised us to contact the appropriate Azure team.

Despite this, Azure App Registration continues to fail domain verification.

Has anyone encountered a similar issue where the validation file is accessible and correctly configured, but Azure is still unable to verify the domain? Are there any backend validation logs, known issues, or additional checks that can be performed?

Any guidance would be appreciated.