GNU Radio Companion 3.7.13.5
Robot Framework 5.0
Python 3.9.12

GNU Radio flowgraph
gr1.jpg

gr3.jpg

Robot code

*** Settings ***
Documentation     GNURadio XMLRPC
Library           RequestsLibrary
Library           OperatingSystem

*** Variables ***
${host}           127.0.0.1
${port}           8270
${freq}           1500
${amplitude}      2
${data}           ${EMPTY}
${path}           c:/temp/setAmp.xml

*** Test Cases ***
TC1
    Log    "Start"
    ${data}=    Get File    ${path}    encoding=UTF-8
    Log    ${data}
    ${response}=    POST    http://${host}:${port}    ${data}
    Log    "End"

setAmp.xml
<?xml version="1.0"?>
<methodCall>
   <methodName>set_amplitude</methodName>
      <params>
         <param>
            <value><double>2.0</double></value>
         </param>
      </params>
</methodCall>

gr4.jpg

gr5.jpg

rf1.jpg
https://i.ibb.co/NxPQ4f5/rf1.jpg