Fonoa vs Quaderno

Fonoa

The API reference is served as Markdown with an OpenAPI definition on each endpoint page, and e-invoicing submissions are idempotent by transaction_id. API keys are issued by Fonoa staff after contact, no price, rate limit or changelog is published, and the only public terms date from May 2020 and cover older seller sites.

Quaderno

A public OpenAPI 3.1 spec covers 92 operations, with a free sandbox and a status page showing no incident since July 2025. The API key has full account access, there are no idempotency keys, and the newest public API version is dated October 2024.

Fonoa

1. Send the key in the Ocp-Apim-Subscription-Key header. Use the sandbox key at https://sandbox.fonoa.com and the production key at https://api.fonoa.com
2. Treat validations and e-invoicing submissions as asynchronous. POST, then poll the GET endpoint or wait for the webhook, and avoid tight polling
3. Reuse the same transaction_id on a retry of /v1/transactions. A transaction already processed is not processed again
4. Commit a calculation with POST /tax/v2/calculations/<uuid>/commit only when the sale is final. The commit adds it to revenue tracking
5. Ask the Fonoa contact to configure webhooks. There is no API for it, and always fetch resource_url as given in the webhook

Quaderno

1. Call GET https://quadernoapp.com/api/authorization first. Its href gives the account subdomain that every other call needs
2. Before retrying a failed POST /transactions, list invoices by processor_id to check whether the sale was recorded. There is no idempotency key
3. Treat GET /invoices/{id}/deliver as a write. It emails the invoice to the customer
4. Correct a final invoice with a credit note. DELETE on invoices returns 410 and PUT accepts only notes, tags, metadata and address fields
5. Read X-RateLimit-Remaining and X-RateLimit-Reset, and page with created_before and limit up to 100