I need some help on 2 points below
1) How I can pull the transaction details from PayPal for a transaction such as Transaction ID, Payment Status, Customer Instructions based on the SessionID (unique identifier) on click of a link. The unique id which I am passing is the SessionID of the user under CUSTOM field.
So, the need is to pull the above mentioned data on a Click of a link.
2) I heard that there is an IPN facility as well and I have got the code to use in Classic ASP but I could not find anywhere including PayPal that whether do I need to schedule this IPN page on the server so that the page checks for the transaction every 15 minutes OR for every transaction, PayPal will call the page automatically and submit the details.
I am using Website Payment Standard and currently using PDT transfer to transmit this data back to my site but there are few customers who after making the payment at PayPal closes down the browser and value does not reach back to the site.
Appreciate your help on 1st point with classic ASP and some information on 2nd point.
1) In short, given your specific situation, you cannot.
You mentioned that you are using Website Payments Standard, so you will not be able to programmatically retrieve transaction details from PayPal. However, if you were to upgrade your account, you could utilize PayPal's GetTransactionDetails API operation to obtain information about a specific transaction by sending a valid transaction ID. You cannot, however, use the SessionID to retrieve transaction details.
2) Paypal automatically sends a notification to your IPN listener when a transaction is affected.
In order to use Paypal's Instant Payment Notification (IPN) services, you must first enable IPN messages from within your Paypal account. If you want to verify whether IPN messages are being sent, or need to re-send them, etc., you may do so from within your PayPal account under IPN History.
Also, IPN messages typically include a corresponding transaction ID (txn_id) that (I think, but not entirely sure) may be used in the GetTransactionDetails API.
My Suggestion → Setup IPN.
Once you've configured IPN properly, store the transaction information from your IPN message into a database. This eliminates the need to upgrade your account and query Paypal for the transaction details. Best of all, IPN is unaffected by whether the user returns to your website or not.