In ArcGIS StoryMaps, when designing a story on the Design tab, the Customize section is unavailable and StoryMaps returns the following error message.
Error: This feature is only available to subscription accounts.
ArcGIS StoryMaps is accessed with an ArcGIS Online public account. Public accounts have access to limited functionality in ArcGIS Online. Full functionality is available to organizational accounts or to individual accounts with an ArcGIS Online subscription. Refer to ArcGIS Online: Accounts for more information.
Use one of the following options to resolve the issue.
Convert the public account into an organizational account
Public account users must request an invitation from an ArcGIS Online administrator to join an ArcGIS Online organization. Refer to ArcGIS Online: Join organization for more information.
Purchase and activate an ArcGIS Online subscription
Purchase and activate an ArcGIS Online subscription to access the full functionality of ArcGIS StoryMaps. Refer to ArcGIS Online: ArcGIS Online Pricing and ArcGIS Online: Activate subscription for more information.
The image below shows that the Customize section is available on the Design tab in ArcGIS StoryMaps when an organizational account user or ArcGIS Online subscription user accesses it.