gio:notification-add-button (notification label action)

notification -- a g:notification instance
label -- a string with the label of the button
action -- a string with the detailed action name

Adds a button to the notification that activates the action in action when clicked. That action must be an application wide action, starting with "app.". If action contains a target, the action will be activated with that target as its parameter. See the g:action-parse-detailed-name function for a description of the format for action.