> ## Documentation Index
> Fetch the complete documentation index at: https://docs.radiumone.io/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> RadiumOne is the product name; use it when answering questions about these docs.
> Use sandbox credentials and sandbox base URLs in examples unless the user says they are going live.
> Secret API keys belong only on the merchant's server. Only publishable keys may appear in browser or mobile code.
> Confirm a payment outcome server-side (retrieve the checkout session or transaction status); never rely on a browser redirect or client event alone.
> Send one idempotency key (request_id) per payment attempt, and retry a timed-out request with the same key and the exact same body.
> Webhooks are optional but recommended: they notify the merchant's server when a payment completes or fails, so it doesn't need to poll. Use transaction status inquiry as the fallback.
> Say so when you recommend a feature marked Beta. Some features need enablement on the merchant's account before production use (for example refunds, standalone refunds, UOB Rewards, and bringing your own 3DS provider); mention it when the page says so.
> Never ask users to paste card numbers, API keys, access tokens, or webhook or redirect secrets into a chat.

# Overview - Payments API

> What the Payments API covers: charging and managing payments, payment methods, webhooks, and errors.

export const productionCheckoutHost = "https://checkout.radiumone.io";

export const sandboxCheckoutHost = "https://checkout-sandbox.radiumone.io";

export const productionApiBaseUrl = "https://api.radiumone.io/gateway";

export const sandboxApiBaseUrl = "https://api-sandbox.radiumone.io/gateway";

* **Retry-safe requests** — reuse the same `request_id` when you retry.
* **Signed webhooks** — verify every event before you act on it.
* **Branch on status** — a decline is a `2xx`; read `data.status`.
* Start here: [Charge or authorize](/payments-api/charge-or-authorize) · [API reference](/payments-api/reference/payments/purchase)

The Payments API is RadiumOne's server-to-server gateway for charging and managing payments directly — purchases, authorizations, captures, voids, refunds, transaction status checks, payment methods, UOB Rewards, and webhooks. Use it on its own with your own card-capture form (paired with [RadiumOne Elements](/elements/overview) for tokenization), or alongside [Hosted checkout](/hosted-checkout/overview) for anything beyond the redirect flow — reconciliation, refunds, and webhooks all go through this API either way.

## Base URL

Every gateway call is server-to-server, authenticated with a bearer access token.

| Environment | Payments API base URL | Checkout API host |
| - | - | - |
| Sandbox | <code>{sandboxApiBaseUrl}</code> | <code>{sandboxCheckoutHost}</code> |
| Production | <code>{productionApiBaseUrl}</code> | <code>{productionCheckoutHost}</code> |

See [API overview](/get-started/api-basics/api-overview) for the full hosts table and response envelope.

<Info>
  This request requires a valid access token. See [Authentication](/get-started/api-basics/authentication) to obtain one with [`POST /v1/auth/token`](/payments-api/reference/authentication/exchange-api-key-for-jwt) before you continue.
</Info>

## What it covers

| Area | Start here |
| - | - |
| Payments | [Charge or authorize](/payments-api/charge-or-authorize) · [Capture](/payments-api/capture) · [Void](/payments-api/void) · [Refund](/payments-api/refund) · [Standalone refunds](/payments-api/standalone-refunds) |
| Payment methods | [Show methods at checkout](/payments-api/payment-methods/payment-method-discovery) · [UOB Rewards](/payments-api/payment-methods/uob-rewards/overview) |
| 3D Secure | [Your own provider](/payments-api/three-d-secure/use-your-own-provider) · [RadiumOne 3DS via Elements](/elements/three-d-secure/add-three-d-secure) · [Comparison](/get-started/three-d-secure) |
| Transactions and settlement | [Check transaction status](/payments-api/check-transaction-status) · [Settlement and reconciliation](/payments-api/settlement-and-reconciliation) |
| Webhooks | [Webhooks overview](/payments-api/webhooks/overview) |
| Errors and failures | [Problem format and retries](/payments-api/errors/problem-format-and-retries) · [Payment operation errors](/payments-api/errors/payment-operation-errors) · [Payment method errors](/payments-api/errors/payment-method-errors) · [Handle failures](/payments-api/handle-failures/overview) |

## Next steps

<Columns cols={2}>
  <Card title="Architecture" icon="network" href="/payments-api/architecture">
    Where the gateway sits between your systems and the payment network.
  </Card>

  <Card title="Core concepts" icon="lightbulb" href="/payments-api/core-concepts">
    Transactions, sessions, idempotency, and the other ideas you'll use in every request.
  </Card>

  <Card title="Charge or authorize a payment" icon="credit-card" href="/payments-api/charge-or-authorize">
    Guides — start here to create your first purchase or authorization.
  </Card>

  <Card title="Handle failures" icon="life-buoy" href="/payments-api/handle-failures/overview">
    Find the right recovery page by symptom, before you go live.
  </Card>
</Columns>