# Implementation notes

Source: <https://docs.gjold.com/notes>

The reference says what each request does. These notes say how to put the requests together so that nothing is lost, nothing happens twice, and nothing breaks under load: the problems we see most often in integrations, and their fixes.

| Note | What it covers |
|---|---|
| [Synchronizing with seq](https://docs.gjold.com/notes/synchronization) | Matching our objects to yours, applying changes by revision, running one synchronization at a time, and what seq guarantees. |
| [Receiving pings](https://docs.gjold.com/notes/pings) | Checking the signature, answering fast, and what to do when pings stop. |
| [Orders and payment links](https://docs.gjold.com/notes/orders) | One link per order, the success page that proves nothing, payments for less than the order, and links that must not be paid. |
| [Retries and idempotency](https://docs.gjold.com/notes/retries) | Requests that time out, keys that make retries safe, and the index that stops two acts from the same state. |
| [Charging subscribers](https://docs.gjold.com/notes/subscribers) | The schedule, failed charges and when to retry them, and getting a new card. |
| [Websites and apps](https://docs.gjold.com/notes/payment-window) | Sending the payer to the payment window and back, and why not in a frame or a WebView. |
| [Moving from v1 to v2](https://docs.gjold.com/notes/moving-to-v2) | The URLs and keys, the stricter requests, the clearer errors, and the requests that are new. |
| [Before going live](https://docs.gjold.com/notes/checklist) | A checklist of all of the above. |

The notes hold for every version of the API. Where the versions differ, a paragraph that starts "In v1," or "In v2," says how. The notes assume the reference, and link to it. Where a rule comes from outside the API, such as how long an authorization lasts, they link to the [knowledge base](https://docs.gjold.com/learn).