Polar.sh Webhook Confirmation Email with Rovela (2026): Standard Webhooks + Idempotency-Key
Verify Polar webhook-id / webhook-timestamp / webhook-signature on the raw body, handle order.paid / subscription.created, and send branded confirmations via Rovela POST /emails with Idempotency-Key = polar-order.paid-{id} or polar-subscription.created-{id}. Polar owns OSS/indie checkout; Rovela delivers. Distinct from Lemon Squeezy, Paddle, and Stripe webhook posts.