add
Starts an add-to-cart app moment.
This method should be called as soon as the user indicates an intent to add an item to their cart.
Return
A moment identifier that can be used to close the add-to-cart moment. If an error was encountered, this method returns null.
Parameters
The ID that represents the item being added to the cart. This value is optional and, if present, will associate the value as a property of the moment.
The number of items being added to the cart. This value is optional and, if present, will associate the value as a property of the moment.
The unit price of the item being added to the cart. This value is optional and, if present, will associate the value as a property of the moment.
A map of Strings to Objects that represent additional properties to associate with the moment. This value is optional. A maximum of 10 properties (not including the ones set via arguments to this method) may be set.