Ouch. Self-answered at point of sending emails. 

Hi @32Gi, 

Thanks for asking this great question! Sorry you had to experience it first to find the answer - as I’m sure you already know now (but to clarify for folks that have this question in the future), you won’t be able to send the emails and will be prompted to upgrade your plan first before it is able to send to additional profiles. You can find out more details on how Klaviyo Bills Customers for Email, and what the rates are for profiles, in this article. I’ve added the Email Billing plans below, for easy reference. For a full overview of these plans and additional instructions/terms, please reference the article link. 
 

It is important to note that we do not provide refunds for downgrades, as outlined in our Terms of Service. When you downgrade, that change takes effect immediately and not at the end of the billing cycle. In addition, the prices outlined in the image above do not include sales tax.

Thanks, 
-Cass.