Courio (sendcourio.com)

Lists which destination countries and service levels Courio can mail a physical paper letter to, with an indicative "from" price (EUR including VAT, 1 black-and-white page), typical delivery time and the legal product name. No account or API key is needed. Call it before quote_letter to check a destination is served; pass a country (ISO 3166-1 alpha-2, e.g. "DE") to narrow the answer. Service levels: "standard" (ordinary mail, no proof), "tracked" (tracking only), "registered" (registered mail: proof of deposit), "registered_ar" (registered with acknowledgement of receipt: proof of delivery, the one to use for legal notices).

Returns the current status of a letter (awaiting_payment, paid, submitted, in_transit, delivered, failed, expired, ...), its timeline and, once available, proof links (proof of deposit for "registered", proof of delivery for "registered_ar"). No account is needed; the letter_id is the credential. Recipient details are partially redacted unless the request carries the API key that created the letter.

Prices a physical letter (printed, enveloped and posted by Courio) and returns a quote_id. Free and commits to nothing: no account, no payment, nothing is mailed. Give the service level, sender and recipient postal addresses, and the document (pdf_base64, pdf_url, or plain/markdown text). The price is in EUR including VAT (set currency to "USD" to also see a USD price), fixed for 24 hours. The document is checked and content-moderated; a problem comes back as an error with a hint. Quotes are capped per day (limit_exceeded with retry_after): reuse a quote_id rather than re-quoting. Service levels: "standard" (ordinary mail, no proof), "tracked" (tracking only), "registered" (registered mail: proof of deposit), "registered_ar" (registered with acknowledgement of receipt: proof of delivery, the one to use for legal notices). The quote gives the estimated delivery time (estimated_delivery_days). Next step: show the price, the legal product and the terms of sale (terms_url) to the human, then call send_letter if they agree.

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Creates the letter for a quote and returns a payment link (Stripe Checkout). No account is needed. YOU CANNOT PAY: show the price and the payment link to the human and ask them to open it and pay. The letter is mailed right after payment and cannot be cancelled or recalled once paid, so paying is the point of no return: make sure the human has seen the price, the recipient and the document first. Calling it again with the same quote_id returns the same letter and link (or its current status once it has been paid). The link expires after about 24 hours. Optionally pass webhook_url (public https) to be notified of status changes. Poll get_letter_status to follow the letter. Autonomous agents whose owner gave them a card through a Stripe Shared Payment Token (e.g. Link) can pay by card themselves with MPP through the REST API (POST /v1/letters with payment_method "mpp", which may be disabled: 422 payment_method_unavailable). Agents that can sign crypto payments can instead pay with x402 through the REST API (POST /v1/letters with payment_method "x402", which may be disabled on this deployment: 422 payment_method_unavailable); official x402 clients cap a payment at $1 by default, so raise the spend limit to cover the quoted price first.