Most of the walk is your systems talking: the shop confirms the order, the warehouse marks it shipped, the carrier's events mark it out for delivery and delivered, and each event triggers one template through the developer API. The picking step sends nothing, on purpose: a customer who gets five messages for one bedsheet starts to block numbers.
The two side paths are where people talk. A missed delivery is a template asking for help, and the customer's reply turns it into a conversation your team can finish in free form. A return starts with the customer, so the whole exchange, label and address included, is a service reply. Neither path needs a promotion, which is just as well: a 901 number cannot receive one.