Get code 4819 when trying to update a contact and the email address is in a different case

Get code 4819 when trying to update a contact and the email address is in a different case

Scenario:

In Zoho the contact has email Xomeemail@test.com

Send an update to 

https://crm.zoho.com/crm/private/json/Contacts/updateRecords {:body=>{:xmlData=>
" <contacts>
  <row no=\"1\">
    <FL val=\"Contactid\">REDACTED</FL>
    <FL val=\"Contact Owner\">REDACTED</FL>
    <FL val=\"First Name\">First</FL>
    <FL val=\"Last Name\">Last</FL>
    <FL val=\"Title\">Title</FL>
    <FL val=\"Account Name\">Account</FL>
    <FL val=\"Email\"> xomeemail@test.com</FL>
    <FL val=\"Billing City\">city</FL>
    <FL val=\"Billing Country\">United States</FL>
    <FL val=\"Billing State\">NY</FL>
    <FL val=\"Billing Zip\">10271</FL>
    <FL val=\"Mailing Street1\">Street</FL>
    <FL val=\"Id\">REDACTED</FL>
 </row>
</contacts>\n", :version=>4, :newFormat=>1, :duplicateCheck=>1, :authtoken=>"REDACTED", :scope=>"crmapi"}, :format=>:json}

You get a response

"{\"response\":{\"result\":{\"row\":{\"error\":{\"details\":\"Duplicate record(s) with same email address already exists.\",\"code\":\"4819\"},\"no\":\"1\"}},\"uri\":\"/crm/private/json/Contacts/updateRecords\"}}\r\n"

Is it not possible to update case?

Thanks