I hope that you have followed all the steps mentioned in this learning path, first of all when you created atlas custom layout you have to make two changes in properties pane. Which are select master layout and scroll behaviour as full widget.
After this there will be option on page "top region" click on this option. After this search for snippet widget in toolbox drag this into in the top region.
Open the created snippet, then add hero header expense building block.
I think so, you are trying to add header in snippet call of Atlas_custom layout page .
You have to make changes in snippet.
Open HeaderExpenses snippet (shown in image) which is present in your Expenses module and then add Hero Header Expense building block in it.