Shopify/active_merchant — pull request #693 by damonmorgan (2013-05-14 15:17:34+00:00)
Title: Add MassPay payment to recipients by UserID

MassPay allows payment to recipients by EmailAddress, UserID or PhoneNumber.
All MassPay items in a single request must use the same field to identify recipients.
https://developer.paypal.com/webapps/developer/docs/classic/api/merchant/MassPay_API_Operation_SOAP/