Best place to start is here https://developer.cisco.com/docs/support-apis/

I’m not sure would need to check  sandbox-iosxr-1.cisco.com228305772257777adminC1sco12345

I just tested this on the devnet sandbox, this format works correctly with the XR device. <?xml version="1.0" encoding="UTF-8"?> <rpc xmlns="urn:ietf:params:xml:ns:netconf:base:1.0" message-id="101"> <get> <filter> <interfaces xmlns="http...

So it closes as it gets something it does not like is my guess, have you tried <?xml version="1.0" encoding="UTF-8"?>?     

Looking at your output, your device successfully process your hello message, this part is ok. But you here are mixing two different netconf framing methods you see in your first attempt, you used the older end-of-message delimiter ]]>]]> (NETCONF 1....