I was shown with a popup message “We’ve noted your change in your estimated number of invitees. Please update the add-on services again.” and I am unsure of how to proceed with my booking.

You received this message because of a change in your estimated number of invitees. This change affects the add-ons to the initial number of party guests.
With the change in number of invitees, we seek your help to reconfirm your add-ons based on the new number of invitees.