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A 409 conflict when creating a contact usually means that a contact already exists in your account with that email address. If you run your XML through RESTClient, it will display the full body output, which might make things a little more clear as well.
If it does end up that this contact already exists, you can always run an update to put the information into the existing contact. You'll just want to be a little careful of how you handle that, as depending on where the form is located, anyone could put any existing email address in and overwrite the existing contact.