Hi,
well, each time a payment is made, send money and mass pay, through API or manually, IPN notify with Customer Values and Masspay Values to AlertURL.
Here is a suggestion about those values;
Customer Values - could maintain the same info
Purchace Values - should include all fees that were paid in the transaction,
ap_totalfeeamount,
ap_totalgrossamount
ap_totalnetamount
Masspay Values - In my opinion you should include in IPN the payment values for each one of the receivers and a global one
ap_status, (status of the overall mass pay request, Complete, Denied or Processed)
ap_receiveremail_X,
ap_status_X, (Completed, Pending, Failed, Unclaimed or Reversed)
ap_paymentgross_X,
ap_paymentnet_X,
ap_paymentfee_X,
ap_referencenumber_X, (this should be a unique traceable transaction ID, good for AP and for the seller to trace the payment)
And for it to be perfect --- all of this could be request remotely through an API encrypted with private and public keys.