A positive response received from server looks as follows:
<packet version="1.4.2.0">
<server>
<lic_install>
<result>
<status>ok</status>
</result>
</lic_install>
</server>
</packet>
A negative response received from server can look as follows:
<packet version="1.4.2.0">
<server>
<lic_install>
<result>
<status>error</status>
<errcode>1020</errcode>
<errtext>The uploaded key file is not valid or does not contain a license key.</errtext>
</result>
</lic_install>
</server>
<output><br />
<b>Warning</b>: Key read error 2: Key test failed in <b>/opt/psa/admin/plib/api-rpc/AgentServer.php</b> on line <b>195</b><br />
</output>
</packet>
Such error is received if the request packet tried to install an invalid license key. The response packet was formed basing on the agent_output.xsd schema, that's why the output node appears.