Once a buyer has been created it's possible to link transactions to that buyer. There are a few ways to associate a transaction to a buyer.
Associate the payment method to a
The easiest way to associate a buyer to a transaction is to pass along a
buyer_id for the payment method when creating a transaction.
This will find a buyer with that
id and associate it to the payment method for
this transaction. If a buyer with that
id could not be found it's ignored.
Alternatively, a transaction can be associated to a buyer by its
external_identifier. If a buyer with that
external_identifier could not be
found it's ignored.