Sub page in the main page module

While I try to include a subpage to the primary page module which through error

Primary module include the subpage like

below code used to access the sub page

Show me your app.module.ts (the @NgModule)
Show me your Primary Page imports please.
And to finish, the nested Component (child)

The above snaps where from my actual project, so I created same workaround in a sample project.
Error message
App module snap

Folder structure
Todo module snap
Todo page snap
Add todo page snap