You won't be able to sort within the activity, but you can pass data into the "custom" parameter (literally called custom) and that would data would show up in the transaction details page in your PayPal account. It would also be returned in IPN, so if you're using that (which I highly recommend) you could easily save the transactions into your own database and then build your own simple system to browse and sort those transactions accordingly. Another option would be to use a combination of TransactionSearch GetTransactionDetails APIs. TransactionSearch will pull a list of transactions in a given timeframe, and then you can loop through those to call GetTransactionDetails for each and display whatever details you need however you need it. The custom data would be available in the GetTransactionDetails response. So the first option would use your own database with automated updates to that database. The second method would simply pull fresh data from PayPal's API as you're using the tool. Either way you would build your own simple front-end management tool to see everything the way you need it. If you need a developer to help with this sort of thing let me know.
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