REST to SOAP Interface: GET request, mapping doesnt work properly

I have a scenario where i am reading the information from the backend system.

Created a Sender Communication Channel which is REST and Receiver Channel is SOAP.

Everything looks good, but when i execute the service via Postman, the value is not being mapped to the SOAP service. However, the SOAP service is getting executed with an error response indicating to pass the input value.

My REST Adapter in SAP PI

Below is the simple Message mapping done. The highlighted fields are the one which are not getting mapped. However, the constant values are getting populated correctly in the SOAP receiver service: -

This is how i am testing via Postman: -

And this the response i get back from the backend.

This shows the whole chain is working fine, except that the main field is not being mapped .

Any help would be appreciated.

Thanks