Error:81115, missing parameter Payment action required?

I keep getting Error:81115, missing parameter Payment action required, when i m开发者_Go百科 doing Doexpresscheckout method? m sending following parameters

&METHOD=DoExpressCheckoutPayment
&VERSION=65.1
&PWD=1299156195
&USER=123hel_1299156185_biz_api1.gmail.com
&SIGNATURE=Ai1PaghZh5FmBLCDCTQpwG8jB264Ay4Ll3wOTnzcWtuD-HdE5qiI1p.N+
&TOKEN=EC-6M866117WG376591R
&PAYERID=RDX5GUURFJ9VY
&PAYMENTACTION=%27.Sale
&AMT=104
&CURRENCYCODE=%27USD.%27,

help me to fix this bug?

Well, a small search made me found 2 possibles solutions for this :

https://www.x.com/message/157458

http://randomerror.wordpress.com/2010/01/27/error-code-81115-on-paypal-express-checkout-code/

The last one seems to be common in PHP app from paypal:

mistake on paypalfunctions.php code

$token = urlencode($_SESSION['token']);
$paymentType = urlencode($_SESSION['paymentType']);

should be:

$token = urlencode($_SESSION['TOKEN']);
$paymentType = urlencode($_SESSION['PaymentType']);

PaymentActionSpecified=true

this field should be set...