String nvpstr = "&TOKEN=" + token + "&PAYERID=" + payerID + "&PAYMENTREQUEST_0_PAYMENTACTION=" + paymentType
+ "&PAYMENTREQUEST_0_AMT=" + finalPaymentAmount + "&PAYMENTREQUEST_0_CURRENCYCODE=" + currencyCodeType
+ "&IPADDRESS=" + serverName;

Having done an earlier call to SetExpressCheckout, I had to change a few parameter names because Paypal had changed it in the documentation but not in the code from the integration wizard.

Now for DoExpressCheckoutPayment I've modified a few but I get a null pointer at strAck:

HashMap nvp = httpcall("DoExpressCheckoutPayment", nvpstr);
String strAck = nvp.get("ACK").toString();
if (strAck.equalsIgnoreCase("Success")) {
    return nvp;
}

Not sure what is wrong, any suggestions for debugging this or possible solutions?