The currently selected shipping option ID. In CreateSession this is the first valid option, in GetSession this is the option that was previously selected (from shipping reference). Used by the frontend to preselect the same option when the user refreshes the checkout page.
{ "shippingId": "string", "sessionId": "string", "selectedOptionId": "string", "settings": { "widgetVersion": "string", "theme": "string", "themeOverride": { … }, "mode": "string", "widthBreakpoints": { … } }, "data": { "options": [ … ], "addons": [ … ], "fields": [ … ], "categories": [ … ] } }