The next step is to integrate this into our existing customer support portal using the XML API. I have managed to create new Requests using the API, including with an initial comment, but I can not add new comments to an existing Request. I can not in fact even update a single field on the Form, even though I'm the application owner (though not the account admin).

Is there a way to add a new comment subform using the Request ID as a field? ie, so I'm not updating the main form, rather just posting another records in the subform table?

This is the update XML:

<ZohoCreator>

    <applicationlist>

        <application name='test-contact-form'>

            <formlist>

                <form name='Bug_Tracker'>

                   <update>

                        <criteria>

                            <field name='ID' compOperator='Equals' value='532891000003224699'></field>

                        </criteria>

                        <newvalues>

                            <field name='Issue_Title' value='New Title'></field>

                            <field name="SubForm_1">

                                <add>

                                    <field name="Comment">An API comment on a new request</field>

                                </add>

                            </field>

                        </newvalues>

                    </update>

                </form>

            </formlist>

        </application>

    </applicationlist>

</ZohoCreator>