Help with REST Api POST Call for CustomData Objects

I'm getting this error after my POST call

[{"type":"EndpointParameterError","parameter":"DuplicateValue","value":"<null>"}]

This is my request

{"type":"CustomObjectData","id":0,"fieldValues":[{"type":"FieldValue","id":"242","value":"2469713031011304819"},{"type":"FieldValue","id":"899","value":"3406107402492215345"},{"type":"FieldValue","id":"241","value":"test@test.com"},{"type":"FieldValue","id":"244","value":"https://"},{"type":"FieldValue","id":"245","value":"http://<elqDomain type=1/>/e/er?s=<span class="eloquaemail">siteid</span>&lid=32008&elq=<span class="eloquaemail">recipientid</span>"},{"type":"FieldValue","id":"982","value":"http://<elqDomain type=1/>/e/er?s=<span class="eloquaemail">siteid</span>&lid=32009&elq=<span class="eloquaemail">recipientid</span>"}],"emailAddress":null,"contactId":6028}