"Content is not allowed in prolog" via /admin/API/mnt/Session/UserName

[CiscoNewb001]

Hello, I am following these docs: https://developer.cisco.com/docs/identity-services-engine/latest/using-api-calls-for-session-management/#detailed-session-attribute-api-calls

Using this CURL request:

curl -X POST -k -H 'Accept: application/xml' -H 'Content-Type: application/xml' -H 'Authorization: Basic REDACTED=' -i 'https://MNT-99.i
se.mydomain.com/admin/API/mnt/Session/UserName' --data 'myuser'

I get back the following error:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<mnt-rest-result>
    <http-code>500</http-code>
    <cpm-code>34110</cpm-code>
    <description>Server has encountered error while processing the REST request</description>
    <module-name>MnT</module-name>
    <internal-error-info>Content is not allowed in prolog.</internal-error-info>
    <requested-operation>Get By Name</requested-operation>
    <resource-id>N/A</resource-id>
    <resource-name>N/A</resource-name>
    <resource-type>FailureReasonList</resource-type>
    <status>SERVER_ERROR</status>
</mnt-rest-result>

My CURL seems to match the docs exactly. What am I doing wrong? No luck in Postman either.

[marce1000]

  - @CiscoNewb001         FYI : https://bst.cloudapps.cisco.com/bugsearch/bug/CSCwk72712
                                  The bug report has a Fixed status but no Known Fixed Releases are mentioned.  That means that developers have fixed the issue, but it is not yet incorporated in a production release.  If the issue is urgent contact TAC and ask for an ETA.

 M.