How to Run a Reference Transaction Using Direct Payment.curl

DoDirectPayment

Request 
-------
Endpoint URL: https://api-3t.sandbox.paypal.com/nvp
HTTP method: POST
POST data:
USER=insert_merchant_user_name_here
&PWD=insert_merchant_password_here
&SIGNATURE=insert_merchant_signature_value_here
&METHOD=DoDirectPayment
&VERSION=86
&PAYMENTACTION=Sale     #Indicates that a payment will be processed
&AMT=10    #The amount of payment
&ACCT=4641631486853053    #The credit card number
&CREDITCARDTYPE=VISA    #The type of credit card
&CVV2=123    #The CVV2 number
&FIRSTNAME=James
&LASTNAME=Smith
&STREET=FirstStreet
&CITY=SanJose
&STATE=CA
&ZIP=95131
&COUNTRYCODE=US
&CURRENCYCODE=USD    #The currency, e.g. US dollars
&EXPDATE=052015    #Expiration date of the credit card

Response
--------
&ACK=Success
&AMT=10%2e00
&CURRENCYCODE=USD
&AVSCODE=X
&CVV2MATCH=M
&TRANSACTIONID=9KK85084958471234    #An ID on which to base a DoReferenceTransaction call
...

DoReferenceTransaction

Request 
-------
Endpoint URL: https://api-3t.sandbox.paypal.com/nvp
HTTP method: POST
POST data:
USER=insert_merchant_user_name_here
&PWD=insert_merchant_password_here
&SIGNATURE=insert_merchant_signature_value_here
&METHOD=DoReferenceTransaction
&VERSION=86
&AMT=2    #The amount of payment
&CURRENCYCODE=USD    #The currency, e.g. US dollars
&PAYMENTACTION=SALE     #Indicates that a payment will be processed
&REFERENCEID=9KK85084958471234     #Use a transaction ID from a DoDirectPayment response

Response
--------
AVSCODE=X
&CVV2MATCH=M
&ACK=Success
&TRANSACTIONID=7TX32596U93391234     #Transaction ID created in this new DoReferenceTransaction call
&AMT=2%2e00
&CURRENCYCODE=USD
...