InDesign SOAP UXP get args & setResult not working

If I run the following soap request, "script.args" is shown as an empty array and the soap response is only "<errorNumber>0</errorNumber>"

But regarding the documentation, this should be working.

<runScriptParameters>
    <scriptText>
        const script = require('uxp').script;
        await app.consoleout(JSON.stringify(script.args));
        return script.setResult('1234');
    </scriptText>
    <scriptLanguage>UXPScript</scriptLanguage>
    <scriptArgs>
        <name>testarg</name>
        <value>123</value>
    </scriptArgs>
</runScriptParameters>

What have I done wrong?