Popup Login Notification for non-logged in users

I've been setting up and configuring the appointment+ plugin for a couple of weeks trying multiple configurations and page shortcode layouts and I'm curious if there was a method to make a popup occur for non logged-in users which contains the login shortcode, or some type of login prompt.

Right now, when users are on the appointment page they can select a day in a month, but then when the time slots of the selected day appear, nothing happens when they are clicked on. Only when a user is logged in that the next step appears.

I feel like there should be something besides the sentence informing a new user an account is required to make/pay for an appointment. It feels broken when nothing happens when clicked on because a user isn't logged in.

Could this be a possibility for a future update?