Thanks for the reply.
1. But these fields are available on the UI, hence must be getting persisted in backend somewhere with relation to the CampaignID, AdGroupID, or AD_ID. On UI we can see the values in AdGroup -> Ad content and must be available in the GET API, hence it must be available in POST API.
2. There must be an object or a field that carries this info, may not be available in GoalOptimizedShoppingAds but must be linked to parent Ad, Parent AdGroup or Parent Campaign Object.
May you please check in the backend where these values are getting saved so that the same can be used in APIs.
Gagan