If true, a payment receipt is sent instead of a statement when
'payment_receipt_email' configuration option is set.
+About the "manual" flag: Normally, if the 'payment_receipt' config option
+is set, and the customer has an invoice email address, inserting a payment
+causes a I<statement> to be emailed to the customer. If the payment is
+considered "manual" (or if the customer has no invoices), then it will
+instead send a I<payment receipt>. "manual" should be true whenever a
+payment is created directly from the web interface, from a user-initiated
+realtime payment, or from a third-party payment via self-service. It should
+be I<false> when creating a payment from a billing event or from a batch.
+
=cut
sub insert {