Your usage now reads as two balances. Sending credits pay for email, one per email. AI credits pay for the AI email editor. A meter for each sits above your account in the sidebar, with what is left and when it resets.
Buying AI credits or changing plan now shows the amount due and the card on file, and charges only when you confirm.
What you need to do. If you read usage from the API, use billing.includedCredits, usedCredits, and overageCredits, which replace the email counts. AI credits have their own includedAiCredits fields.