Redeem a Loppee-issued subscription coupon for a business you manage: runs the exact same validation as validate_coupon, then creates a Stripe Checkout session for the chosen paid plan WITH the discount already applied, and returns its url plus the priced breakdown (original_cents, discount_cents, final_cents) and a redemption_id. IMPORTANT: this tool never charges anyone — the business owner must open the returned url and complete payment on Stripe's hosted page; until then the redemption is 'pending' and is released automatically if the checkout expires. Redeeming counts against the code's redemption limits while pending, so do not call this speculatively — use validate_coupon to check a code. Retry-safe/idempotent for an identical pending business + code + tier + period: it returns the same redemption and live Checkout session instead of creating another. A different plan, period, or coupon is refused with billing_checkout_in_progress while the existing business Checkout remains open; no competing session is created. Requires a scoped management key whose account_id + business_id match and whose allowed_actions include redeem_coupon (owner opt-in), plus enabled online billing (billing_not_configured otherwise); call get_agent_identity first. Machine-readable failures match the owner UI exactly: coupon_not_found (invalid code), coupon_inactive, coupon_expired, coupon_wrong_plan (code is scoped to a different plan), coupon_exhausted (total redemption cap reached), coupon_customer_limit (this business already used it), coupon_requires_paid_plan, plus the standard management auth errors (missing_api_key / forbidden_account / management_rate_limited), billing_already_active, billing_checkout_in_progress, and billing_not_configured. A coupon changes the subscription PRICE only. It never changes verification class, review reputation, plan entitlement, eligibility, or quality band; completed payment grants exactly the chosen plan.