Pro Sites thank you page query string

I am using Pro Sites and need to understand a bit more about the thank you page query string after a successful transaction has gone through.

For completed transactions the 'my-account' page displays a url ending with something like (numbers have been randomized they aren't from real transactions!):

/my-account/?bid=33&action=complete&token=EC-5VS123456A123456A&PayerID=1ABCD1ABCFRT7

What is the significance of the 'token' and 'PayerID' query string variables? Are these BOTH unique for every successful checkout transaction?

Any help would be appreciated as I need to use one or both of these query variables to add to an affialiate tracking pixel.