Our current system flow on closing a transaction day is by showing a yes-no message box that informs the user if it will close a particular transaction day. But still some users made mistakes and confuse about the flow. Here is the message using the UI wireframe.
download bmml source – Wireframes created with Balsamiq Mockups
Should I make double messagebox to ask the user if they are really sure? Use a bigger fontsize? Or a new sequence of steps.