Failing invoice update in Xero

Request

<?xml version="1.0" ?>
<Invoice>
  <Type>
    ACCREC
  </Type>
  <InvoiceNumber>
    INV-0029
  </InvoiceNumber>
  <Reference>
    invoice_123
  </Reference>
  <Contact>
    <ContactID>
      2e68080d-b3bd-4051-b33c-9f031550b958
    </ContactID>
    <Name/>
  </Contact>
  <Date>
    2011-09-21T00:00:00
  </Date>
  <DueDate>
    2011-09-30T00:00:00
  </DueDate>
  <LineItems>
    <LineItem>
      <Description>
        Icecream
      </Description>
      <Quantity>
        12
      </Quantity>
      <AccountCode>
        200
      </AccountCode>
      <LineAmount>
        132
      </LineAmount>
    </LineItem>
  </LineItems>
  <Status>
    SUBMITTED
  </Status>
</Invoice>

Response

<?xml version="1.0" ?>
<ApiException xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
   
  <ErrorNumber>
    10
  </ErrorNumber>
   
  <Type>
    ValidationException
  </Type>
   
  <Message>
    A validation exception occurred
  </Message>
   
  <Elements>
     
    <DataContractBase xsi:type="Invoice">
       
      <ValidationErrors>
         
        <ValidationError>
           
          <Message>
            Paid to name cannot be empty.
          </Message>
           
        </ValidationError>
         
        <ValidationError>
           
          <Message>
            Contact cannot be empty.
          </Message>
           
        </ValidationError>
         
      </ValidationErrors>
       
      <Warnings/>
       
      <Contact>
         
        <ValidationErrors>
           
          <ValidationError>
             
            <Message>
              Contact cannot be empty.
            </Message>
             
          </ValidationError>
           
        </ValidationErrors>
         
        <ContactID>
          2e68080d-b3bd-4051-b33c-9f031550b958
        </ContactID>
         
        <ContactNumber>
          None
        </ContactNumber>
         
        <ContactStatus>
          ACTIVE
        </ContactStatus>
         
        <Name/>
         
        <Addresses>
           
          <Address>
             
            <AddressType>
              POBOX
            </AddressType>
             
          </Address>
           
          <Address>
             
            <AddressType>
              STREET
            </AddressType>
             
          </Address>
           
        </Addresses>
         
        <Phones>
           
          <Phone>
             
            <PhoneType>
              DDI
            </PhoneType>
             
          </Phone>
           
          <Phone>
             
            <PhoneType>
              DEFAULT
            </PhoneType>
             
          </Phone>
           
          <Phone>
             
            <PhoneType>
              FAX
            </PhoneType>
             
          </Phone>
           
          <Phone>
             
            <PhoneType>
              MOBILE
            </PhoneType>
             
          </Phone>
           
        </Phones>
         
        <UpdatedDateUTC>
          2011-09-21T12:27:55.65
        </UpdatedDateUTC>
         
        <ContactGroups/>
         
        <IsSupplier>
          false
        </IsSupplier>
         
        <IsCustomer>
          true
        </IsCustomer>
         
      </Contact>
       
      <Date>
        2011-09-21T00:00:00
      </Date>
       
      <DueDate>
        2011-09-30T00:00:00
      </DueDate>
       
      <BrandingThemeID xsi:nil="true"/>
       
      <Status>
        SUBMITTED
      </Status>
       
      <LineAmountTypes>
        Exclusive
      </LineAmountTypes>
       
      <LineItems>
         
        <LineItem>
           
          <ValidationErrors/>
           
          <Description>
            Icecream
          </Description>
           
          <UnitAmount>
            11
          </UnitAmount>
           
          <TaxType>
            OUTPUT
          </TaxType>
           
          <TaxAmount>
            10.89
          </TaxAmount>
           
          <LineAmount>
            132
          </LineAmount>
           
          <Tracking/>
           
          <Quantity>
            12
          </Quantity>
           
        </LineItem>
         
      </LineItems>
       
      <SubTotal>
        132
      </SubTotal>
       
      <TotalTax>
        10.89
      </TotalTax>
       
      <Total>
        142.89
      </Total>
       
      <UpdatedDateUTC>
        2011-09-22T02:08:09.443
      </UpdatedDateUTC>
       
      <CurrencyCode>
        USD
      </CurrencyCode>
       
      <FullyPaidOnDate xsi:nil="true"/>
       
      <Type>
        ACCREC
      </Type>
       
      <InvoiceID>
        651fd624-9663-48c7-bdaa-6694c8ff40f8
      </InvoiceID>
       
      <InvoiceNumber>
        INV-0029
      </InvoiceNumber>
       
      <Reference>
        invoice_123
      </Reference>
       
      <Payments/>
       
      <CreditNotes/>
       
      <AmountDue>
        142.89
      </AmountDue>
       
      <AmountPaid>
        0.00
      </AmountPaid>
       
      <AmountCredited xsi:nil="true"/>
       
      <SentToContact>
        false
      </SentToContact>
       
      <CurrencyRate>
        1.000000
      </CurrencyRate>
       
    </DataContractBase>
     
  </Elements>
   
</ApiException>