Xml rpc update on a field in a form with subforms failed

Xml rpc update on a field in a form with subforms failed

Hi i am trying to update field in a form with couple of subforms.
When i try to update the field after payment i get weird errors that are not related with the form i am trying to update, but instead it is related with subform in this form.
I tried removing this subform but then it gives me same error with the next subform in the form.

My question is, does zoho suports update on a form with subforms ??
Or this is some other issue. I checked the code multiple times and there are no errors in it.
This is the sample code:
 
 $this->XMLString = "XMLString=<ZohoCreator>
        <applicationlist>
            <application name='" . $this->applicationName . "'>
                <formlist>
                    <form name='" . $this->formname . "'>
                      <update>
                             <criteria>
                                <field name='ID' compOperator='Equals' value='" . $zohoID . "'></field>
                             </criteria>
                             <newvalues>
                               <field name='status' value='Paid'></field>";
                                  $this->XMLString .= "<field name='payment_id value='" . $pp_id . "'></field>";
                              </newvalues>
                       </update>
                    </form>
                </formlist>
            </application>
        </applicationlist>
    </ZohoCreator>";

And this is the response i get:

<response>
  <result>
    <form name="ACN_Registration">
       <update>
           <criteria>
               <field compOperator="Equals" name="ID" value="xxxxxxxxxxxxxxxxxxx"/>
            </criteria>
             <newvalues>
                   <field name="status" value="Paid"/><field name="pp_id" value="1524565"/>
                   <field name="amount" value="100"/>
             </newvalues>
              <status>
                   Failure, The entry 'xxxxxxxxxxxxx' already exist for the field 'Field name here'
            </status>
      </update>
  </form>
 </result>
</response>