It would be helpful to refactor Addresses in your services (specifically/e.g.: Zoho Invoice Customer Details)
So that the address elements in the Response are more obviously typed as Address. I think this would improve the clarity of your service(s) and it would help with the (de)serialization.
E.g. The service currently returns:
<BillingAddress>B-1104, 11F, Horizon International Tower, No. 6, ZhiChun Road, HaiDian District,</BillingAddress> <BillingCity>Beijing</BillingCity> </BillingState> <BillingZip>100088</BillingZip> <BillingCountry>China</BillingCountry> <BillingFax>+86-10-82637827</BillingFax> <ShippingAddress>4900 Hopyard Rd, Suit 310</ShippingAddress> <ShippingCity>Pleasanton</ShippingCity> <ShippingState>CA</ShippingState> <ShippingZip>94588</ShippingZip> <ShippingCountry>USA</ShippingCountry> <ShippingFax>+1-925-924-9600</ShippingFax>
I think it would be better like this:
<BillingAddress>
<Address></Address>
<City></City>
<State></State>
<Zip></Zip>
<Country></Country>
</BillingAddress>
<ShippingAddress>
<Address></Address>
<City></City>
<State></State>
<Zip></Zip>
<Country></Country>
</ShippingAddress>
In our code, both types would be more easily represented as derived from the same type 'Address'.