How to update a boolean field via XML RPC API

How to update a boolean field via XML RPC API

Hello,

how would I pass a boolean value to the XML RPC API, if I want to update a boolean field (Decision box)?

When I use the following XML

<ZohoCreator>
    <applicationlist>
        <application name='TestApp'>
            <formlist>
                <form name='TestForm'>
                    <update>
                        <criteria>
                            <field name='ID' compOperator='Equals' value='519261000000601003'></field>
                            <reloperator>AND</reloperator>
                        </criteria>
                        <newvalues>
                            <field name='BoolField' value='true'></field>
                        </newvalues>
                    </update>
                </form>
            </formlist>
        </application>
    </applicationlist>
</ZohoCreator>

then I get back an error

<error>
  <code>2902</code> 
  <message>
    <![CDATA[ Invalid column value &quot;true&quot;specified]]> 
  </message>
</error>

How else would I pass a boolean value? Passing 0 or 1 gives me the same error.

Thank you in advance,
Ute