The following message may be returned when exporting a template from a Web AppBuilder application:
"Exported succcessfully! However, it appears that you don't have permission to share the template item to the template group specified in your organization.
You need to manually add it to the group once it is accessible."
This message appears when Portal for ArcGIS or ArcGIS Online is configured with the Default Configurable Apps group. This group contains all of the default application templates used to make apps, but it is not possible to share additional templates with the group.
If Portal for ArcGIS or ArcGIS Online is configured with the Default Configurable Apps group, a custom group must be created and set as the Configurable Apps group. You can also share the default templates with the custom group as well, so that end users can also have those as options when creating apps.
Please see the below workflow: