I'm trying to convert a lead to account and contact using method https://www.zoho.com/crm/help/api/convertlead.html.

And while account and contact already exists then also associated accountid and contactid have been added to xml request.

Request example

  https://crm.zoho.com/crm/private/json/Leads/convertLead?version=1&scope=crmapi&leadId=1479825000000089009&authtoken=xxxxx&newFormat=1&xmlData=<Potentials><row no="1"><option val="createPotential">false</option></row><row no="2"><FL val="ACCOUNTID">1479825000000088001</FL><FL val="CONTACTID">1479825000000089005</FL><FL val="OVERWRITE">false</FL></row></Potentials>

And the response is:

{"response": {"uri":"/crm/private/json/Leads/convertLead","error": {"code":4819,"message":"Duplicate record(s) with same email address already exists."}}}