An i-WAT ticket is a digitized version of a WAT ticket.
In i-WAT, messages signed in GnuPG (i-WAT messages) are exchanged among the participants to transfer i-WAT tickets.
Each trade takes three steps: sending (by the sender) -> acceptance (by the receiver) -> approval (by the drawer), because in computer networks communications are asynchronous1, and because every copy of a digital data is genuine and indistinguishable from each other. We need to provide a way for the participants to confirm each other's intent by replying to messages, and to guarantee that the same ticket is not used multiple times by a malicious user.
The copy of an i-WAT ticket at the drawer's i-WAT book always indicates the approved holder of the ticket.
Communications being asynchronous in this context means that sending and receiving of a message does not occur at the same time.