In Growth, when Meta takes a campaign message and later reports it failed, that person now shows Failed with Meta’s reason, and the campaign counts them as failed, not sent. The list says “Sent to N · M failed”, or “Not sent · M failed” when Meta took nobody; a campaign that reached nobody is marked Failed.
When Meta refuses because of a payment or account setup issue on your WhatsApp Business account, there is one notice — on the campaign and under Recently sent in Account › Notifications, never by email: “Your WhatsApp messages aren’t being delivered”, three steps, and one button, Fix it at Meta, that opens the page Meta named. Send a test sends the campaign to your own number; Meta charges a test like any other message. Meta’s own words are under Details from Meta.
Since 9 October the campaign’s detail shows the message As it went out, the copy in the customer’s conversation turns failed with Meta’s reason, and Customers › All customers shows Failed before a last message of yours that did not go out.