Creating a field - Studio?

Hi team,

I am trying to work with customerContractIn web service for SAP BY Design, in this web service I do not have access to a filed called "external reference" since I read that I can not enable this field to be called from the web service I thought I could simply extend a field and duplicate the data of "external reference into my new extended field which I can then expose in my web service using the Adapt option.

I help in the matter would be greatly appreciated.