Get the organization's credit balance: monthly credits (reset each billing period) and pack credits (purchased, never expire). Audits spend credits pay-as-you-go while they run; run_audit shows an upper-bound estimate before starting. An audit costs 50 credits plus 2 per audited page, however the page is fetched, plus 1 per distinct external link the cloud checks when external link checking is on. A balance under 52 (a one-page audit) cannot start one, and a balance that covers fewer pages than requested starts a smaller audit. Read-only.