What counts as an API request?

Only calls to the validation endpoint (/v1/vat/:vatId) count against your monthly quota. The VAT rates endpoint (/v1/rates) and dashboard/account API calls are free and don't count. A malformed request rejected as INVALID_FORMAT, a VIES_UNAVAILABLE outage, and a quota-exceeded 429 are not charged — only requests that return an actual valid/invalid determination consume a quota slot. Every response carries RateLimit-* headers so you can track exactly how many requests you have left without checking the dashboard, and the pricing page lists the monthly quota for each plan.