https://hostname.example.com:2087/cpsess##########/json-api/unsetupreseller?api.version=1&user=username

https://hostname.example.com:2087/cpsess##########/xml-api/unsetupreseller?api.version=1&user=username

whmapi1 unsetupreseller user=username

{
  "metadata": {
    "version": 1,
    "reason": "OK",
    "result": 1,
    "command": "unsetupreseller"
  }
}

<result>
    <metadata>
        <version>1</version>
        <reason>OK</reason>
        <result>1</result>
        <command>unsetupreseller</command>
    </metadata>
</result>