How can I receive a notification when a customer fills out a signup form?
At this time, Klaviyo does not have a built-in notification that you can receive when a customer fills out a signup form. If you would like to receive a notification, you can CC or BCC the desired email on the first message of a flow triggered by the list your customer joins when filling out the form. You will add this CC or BCC on the content page for the first email of the flow.
When the customer fills out your form and joins your list, they will enter the flow and receive the first email of the flow - you will then receive that email as well to your inbox notifying you of the customer subscription to your list.