What could be the reason behind the failure of XML api & format=xml response after upgrading IIS server to 2019?

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There could be several reasons behind the failure of XML API and format=XML response after upgrading IIS server to 2019. Here are some possible explanations:

1. Configuration issue: It's possible that the new IIS server is not configured properly to handle XML requests and responses. This could be due to changes in the configuration settings or the absence of necessary modules and features.

2. Compatibility issues: When upgrading to a new version of IIS, there could be compatibility issues with the existing code or applications. XML APIs and responses might be affected by these changes.

3. Security settings: The security settings for the new IIS server might be more restrictive than the previous version, which could be preventing XML requests and responses from being processed.

4. Firewall settings: The firewall settings could be blocking XML requests and responses, which could be causing the failure.

5. Network connectivity: There could be network connectivity issues between the client and server, which could be causing the failure of XML API and format=XML response.

In order to diagnose the exact cause of the issue, it's recommended to examine the IIS server logs and error messages, as well as checking the configuration settings and security policies.