Purchased credits carry over until used. Included credits renew for the allowance period shown on your account. Unused included credits do not accumulate. A Blog Site owner or admin can open Billing → Your credits for the balance and renewal date. If you are an editor, ask your owner or admin to check.
If a paid AI action needs more credits than you have, you can wait for renewal, buy a credit pack if your account offers it, or use a supported model on your own provider account. The provider may charge you for that work. You can still edit manually, and running out of AI credits does not take published posts offline.
See current plan options or how to connect your own provider.