If you're using Eikon, you can use RDP Library to retrieve market data for any RIC including USGN3015=RR. See the Quick Start for .NET edition of RDP Library. Also check out the article titled "Discover our Refinitiv Data Platform Library", which describes RDP Library and provides links to C# code samples.
Thank you this helps a lot !!! Now, I just need to figure out the access denied/missing scope issue.
You posted this question under the "Eikon Data API" forum.
However, this Eikon Data API does not provide REST API document.
The API is supported in Python.
If you are using other products, please provide the product name.