Please check the following if you have a member that has accepted their invitation, and been granted access to Expense, but shows as Invited in Expense and cannot be added to approval routes.
Close the Expense tab and reopen it. This will re-synchronise the app in the event that the user accepted their invitation while Expense was open.
Try toggling the member's role in Expense to NO ACCESS and back. This may refresh the link.
Deactivate the member, and then reactivate them in the Members area. Please note that this will remove all role permissions and they will need to be added again.