A product affiliation to designate a supplying company or brick and mortar store location
affiliation: undefined | string;
Coupon code for a purchasable item.
coupon: undefined | string;
shipping: undefined | number;
tax: undefined | number;
A single ID for a ecommerce group transaction.
transaction_id: undefined | string;
A context-specific numeric value which is accumulated automatically for each event type. Values
can include revenue, distance, time and points. When a value is set, the accompanying
parameter should also be defined.
value: undefined | number;