See that the shipment type is TBD in the response body of your POST.
Use Shipments / Update to PUT to /v9/shipments/78817 to indicate that you will be transferring the tickets to an email address supplied in the response body of this PUT.
See in the response body that a new shipment (78826) has been created and returned and that the email address and name to which you should transfer the tickets is provided.
Transfer the tickets to the provided email address (email@example.com in this example) and name (Moe Szyslak in this example).
Simply use Shipments / Complete to PUT to /v9/shipments/78826/complete and supply the transfer URL (if you have one) and mark the shipment and order complete. As of 2018-11-29 you may optionally include a URL to claim the tickets with your TM Mobile complete request. Including the URL will reduce the need for you to be contacted if the recipient does not receive the transfer email from the primary box office.
Transfer Flash Seats tickets to a provided email address