Using Tab Key as a modifier in custom keyboard shortcut

I am trying to add some Touch Bar buttons for actions in the Asana web app. These use the TAB key for the keyboard shortcuts (e.g. TAB + N for a new task). I am unable to use TAB as a modifier key in defining the Custom Keyboard Shortcut — if I hold down TAB and a letter only the TAB symbol is added. Any ideas?

These are some of the keyboard shortcuts for reference:

Any ideas here? I have the same problem