# Guides Integration guides for Syntch: how the pieces fit together, what to send, and what comes back. Each one is written for a developer, so it carries requests and payloads rather than walkthroughs of the administration screens. ## Concepts - [How timezones are handled](https://devportal-simpay-sbx.winkpg.io/docs/guides/how-timezones-are-handled.md): The UTC storage model, the display conversion boundary, and the timezone policy applied to API payloads, exports, and generated documents. ## Integration - [Getting started with the API](https://devportal-simpay-sbx.winkpg.io/docs/guides/api-getting-started.md): Find the API reference, create an API key, authenticate your first call, and handle idempotency, rate limits, and timestamps correctly. - [Rate limits and your allowance](https://devportal-simpay-sbx.winkpg.io/docs/guides/rate-limiting.md): See the limits that apply to your API keys, watch how much allowance is left, find the calls that were refused, and back off correctly when you run out. - [API key expiration reminders](https://devportal-simpay-sbx.winkpg.io/docs/guides/api-key-expiration-reminders.md): How Syntch warns a key's owner ahead of API key expiry, and how to route those warnings to email, a webhook, or another channel your team reads. - [Webhook integration](https://devportal-simpay-sbx.winkpg.io/docs/guides/webhook-integration.md): Receive, verify, and deduplicate Syntch platform events at your own HTTPS endpoint. - [Reusing a stored payment method with payment tokens](https://devportal-simpay-sbx.winkpg.io/docs/guides/reusing-saved-cards.md): Capture the reusable payment token returned when a card is saved, then charge the stored card again without handling card data, declaring whether the customer is present for each charge. - [Storing a card for a wallet](https://devportal-simpay-sbx.winkpg.io/docs/guides/storing-a-card-for-a-wallet.md): Store a card without charging it by creating a save-only session from your server, mounting it, and binding the resulting payment token on the card-saved webhook rather than on what the browser reports. - [Sharing payment tokens across merchants](https://devportal-simpay-sbx.winkpg.io/docs/guides/sharing-payment-tokens-across-merchants.md): Let merchants under one reseller charge each other's stored payment tokens, and learn which handle, which credential, and which consent that takes. - [Hosted payment page iframe integration](https://devportal-simpay-sbx.winkpg.io/docs/guides/hpp-iframe-integration.md): Embed the Hosted Payment Page in an iframe and communicate over the postMessage lifecycle protocol. - [Processor routing and failover](https://devportal-simpay-sbx.winkpg.io/docs/guides/processor-routing-and-failover.md): How Syntch picks a processor for each transaction, when it retries on a second one, and how to read the routing decision for a sandbox transaction. - [Sandbox test cards](https://devportal-simpay-sbx.winkpg.io/docs/guides/sandbox-test-cards.md): One scenario per sandbox classification test card, with the request to send, the classification to expect on the response, and the behavior each card lets you observe. - [The embedded payments SDK](https://devportal-simpay-sbx.winkpg.io/docs/guides/embedded-payments-sdk.md): Mount the hosted payment form inside your own page with the browser loader: options, events, session lifecycle, script pinning, and Content Security Policy. - [Embedded payments compared with in-page card collection](https://devportal-simpay-sbx.winkpg.io/docs/guides/embedded-payments-vs-direct-card-scripts.md): How a gateway-hosted embedded payment form differs from a direct card-collection script, and what changes for your servers when you move. ## Payments - [Transaction lifecycle and settlement](https://devportal-simpay-sbx.winkpg.io/docs/guides/transaction-lifecycle-and-settlement.md): What authorized, captured, and settled mean, when the money actually moves, and which undo operation to use. - [Understanding declines and rejections](https://devportal-simpay-sbx.winkpg.io/docs/guides/understanding-declines-and-rejections.md): How to read a refused payment: the three result fields, the refusal families, which ones leave a hold, what you can retry, and what to tell the payer. - [ACH payments](https://devportal-simpay-sbx.winkpg.io/docs/guides/ach-payments.md): How a bank debit clears, where to take one, and how to read its status from submission through settlement or return. - [Card-present payments over the API](https://devportal-simpay-sbx.winkpg.io/docs/guides/card-present-payments-over-the-api.md): What a terminal application sends on the transactions API for a magnetic stripe, chip, or contactless read, which reader encryption needs setup first, how to identify the terminal, and how to attribute a webhook to it. - [Refunds, voids, and reversals](https://devportal-simpay-sbx.winkpg.io/docs/guides/refunds-voids-and-reversals.md): Undo a payment over the API: which of the three operations applies, how partial amounts work, and the error codes to branch on. - [Transaction custom fields](https://devportal-simpay-sbx.winkpg.io/docs/guides/transaction-custom-fields.md): Define your own fields, collect them on a payment page or through the API, and carry them on the transaction record. ## Quickstart - [Quickstart: Direct API](https://devportal-simpay-sbx.winkpg.io/docs/guides/quickstart-direct-api.md): Authenticate with an API key and take your first card payment over the Syntch API. - [Quickstart: Hosted payment page](https://devportal-simpay-sbx.winkpg.io/docs/guides/quickstart-hosted-payment-page.md): Create a hosted page, open a session for one payment, and send the payer to it without card data touching your server. - [Quickstart: Embedded payments SDK](https://devportal-simpay-sbx.winkpg.io/docs/guides/quickstart-embedded-payments-sdk.md): Mount the Syntch payment form inside your own checkout page with the browser loader. - [Quickstart: Webhooks](https://devportal-simpay-sbx.winkpg.io/docs/guides/quickstart-webhooks.md): Stand up an endpoint that verifies a Syntch delivery signature, register it, and receive your first event. ## See also - [All documentation](https://devportal-simpay-sbx.winkpg.io/llms.txt): the machine-readable index of every public page on this site.