If the error message shows Authorization role is missing then it seems that you have not provided correct credential.
I guess currently you are giving end user credential( byd frontend user), this credential is not required for Webservice.
You have to create a Communication System and Communication arrangement(Goto Application and user management WoC), you can select communication scenario from the system.
for better understanding about webservice follow the guide (https://help.sap.com/studio_cloud)
Hope this will help
Sunil