The default GML link generated by the layer preview page uses WFS 1.0.0 as protocol and GML2 as output format, but this does not work for app-schema layers, since GML2 does not support complex features at all.
Clicking on the link results in a ServiceException response with the following error message:
Ideally, the generated GML link for app-schema layers should:
- use WFS 1.1.0 as protocol
- use either GML 3.1.1 or GML 3.2 as output format, depending on the schema
- use the global OWS service instead of virtual services, to avoid problems accessing secondary namespaces