Since the Agency account is intended for developing for clients, you will not be able to deploy the app to live (they will be password-protected) and you will not have access to JSON import/export. Once you transfer ownership to your client, they’ll be able to upgrade to their preferred app plan and deploy it to live.
When transferring an app from an agency plan to a client, the app reverts to the Free Plan, regardless of its previous plan or deployment status. The new owner must manually subscribe to a paid plan to regain paid features and full live deployment capabilities. Additionally, apps upgraded to their own paid plan stop sharing limits with the agency account and adopt the limits and features of the new plan.