FreshBooks API vs Pennylane

FreshBooks API

OAuth scopes split read and write per resource, such as user:invoices:read. Rate limits have no numbers, status code or headers.

Pennylane

The v2 API has per-resource read and write scopes, an OpenAPI definition on every reference page, llms.txt and a breaking-change process that ran over 24 weeks. Access needs a paid Essentiel plan or partner approval, creation endpoints are not idempotent, and the API agreement lets Pennylane change or revoke the API without notice.

FreshBooks API

1. Call /auth/api/v1/users/me first and keep both ids. Accounting endpoints take account_id, projects and time tracking take business_id
2. Serialise token refreshes. Issuing a new refresh token kills the old one at once
3. Mark an invoice as sent (action_mark_as_sent) or email it. Reports ignore drafts
4. Send x-api-version: 2023-09-25 on journal entry calls
5. Back off on any throttling response yourself. There's no Retry-After to read and no published limit

Pennylane

1. Call GET https://app.pennylane.com/api/external/v2/me first to confirm the token, user and company context
2. Stay under 25 requests per 5 seconds per token and wait for the retry-after value on a 429
3. Do not retry a create after a timeout without checking first. Only supplier invoice imports are deduplicated
4. Send filter and sort again with every cursor. The cursor stores position only
5. Send amounts as strings such as "120.00", and ask for :readonly scopes when the task only reads
6. Use the MCP server for reads only. It cannot create, edit or delete, and firm connections need company_id