Host Header being dropped in API Gateway Straight Through Routing

API Gateway 10.11

Trying to invoke a REST API to call a native service that expects Host Header. When the request to native service is done, it fails with 403 (Forbidden) as the native service is expecting Host header.

With API tracing, able to notice that the Host header is missing in the request to native service Tried executing policy - Custom HTTP Header and Request Transformation to add the Host Header explicitly, the policy status shows success and the output/policy execution indicates that the Host header is present. But straight through routing to the native service fails and the request header has no Host header.
Adding a custom header either at Custom HTTP Header or Request Transformation, shows the added Header in the Request headers to native service call. {Example: Added a custom HTTP header, Header: MyHeader Value: TestHeader , and able to see this in the Request Header of the request to native service}.
Is there any reason why API Gateway is dropping the Host Header. Is there any way to make the Host header as part of the Request Header to native service.
Thanks in advance.

Please post the scrrenshots as well.