var api = XeroApiHelper.CoreApi();

        api.SummarizeErrors(false);

        var invoices = new List<Invoice>();
        var invoicep = new List<Invoice>();

        int i = 1;
        do
        {
            invoicep = api.Invoices.Where("Contact.ContactID == Guid("" + xeroId + "")").Page(i).Find().ToList();
            invoices.AddRange(invoicep);
            i++;
        } while (invoicep.Any());