Not getting expected result using 'webservicequery'

I am trying to call a web service in an expression rule using 'webservicequery' function.

I am passing below headers in the request but in response I am seeing those header values as null (Header values are not getting passed through 'webservicequery' function).

But when I call same web service using 'call web service' node in a process model, it is giving proper response.

Putting below the screenshots of expression where I am using webservicequery' function and call web service node of the process model.

Any pointers on how to resolve this would be very helpful.

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