Record a Paddle refund or an invoice credit note (dobropis).

Writes a negative credit_grants row linked to the sale it reverses: the balance and total_credits_purchased go down, revenue reporting nets the money off, and total_credits_used is untouched because nothing was consumed. An admin clawback cannot do this — it books as consumption.

Idempotent on (provider, provider_txn_id) like /v1/billing/credits: a retry returns the original refund with credited: false.

Rejections: 404 original_grant_not_found; 422 refund_mismatch (other tenant or currency), refund_exceeds_original (cumulative refunds would pass the sale's credits or money), idempotency_key_reused; 409 insufficient_balance when the tenant has already burned the credits — resend with fewer credits and refund the rest as money only.

{"tenant_id": "acme", "credits": 10000, "currency": "EUR",
 "gross_amount_minor": 2000, "provider": "invoice",
 "provider_txn_id": "DOB-2026-001",
 "reverses_provider_txn_id": "RAC-2026-004"}