New guides: Errors and Testing your integration

Errors lists the status codes the App Developer API returns, with the exact error bodies and how to handle each one:

• 401 with invalid_request means no token was found: send it in the X-Yotpo-Token header. 401 with invalid_token means the token can't be used, usually because the merchant uninstalled your app.
• 404 with no Route matched with those values means the path or HTTP method isn't served. A wrong method returns 404, not 405.
• Token endpoint errors and storefront errors, including why an unknown product ID returns 200 with no reviews.

Testing your integration explains how to test without a sandbox: which calls are safe to repeat, which ones change data or can reach shoppers (such as fulfillment updates and loyalty point changes), and a checklist before you go live.

Also fixed: Guidelines and Conventions said the API supports HTTP. Use HTTPS: http:// requests are redirected, and a redirected POST can fail.