does both google checkout and paypal return a transaction id?

Question

once the user has paid using either google checkout or paypal, do you get a response back with the transaction id?

can you then use their api to pull details on the transaction later on for reports?

Answer 1

If you use the appropriate API, yes.

Answer 2

Paypal uses a variable called TXN_ID (Transaction ID) for each transaction that is accessible to you when you turn on IPN (Instant payment notification).

IPN examples can be found at: https://www.paypal.com/us/cgi-bin/webscr?cmd=p/pdn/ipn-codesamples-pop-outside

Fairly comprehensive manuals are all available at the Paypal site, although I found them at times to be a bit confusing, there are some sites out there that offer alternative tutorials on integration (although, treat them with suspicion always and double check against the paypal API).

Along with txn_id, lots more variables about the transaction are returned for you to store and refer to at a later date, and some limited queries can be run or will be sent to you if variables in the transaction changed. (For example, a payment that got declined was retried and succeeded.)