You can now test incremental authorisation end-to-end in the Sandbox environment - including authorised, declined, and failed increment outcomes - before going live.

## Test all increment outcomes in Sandbox

Since [we launched Incremental authorisation](/blog/2026-02-05-incremental-authorisation) in February, the biggest gap was the ability to test it properly in Sandbox before integrating into production. That's now possible.

Sandbox support for incremental authorisation uses a **delta-based trigger model**: the outcome of each increment is determined by the difference between the `amount` you send in the increment request and the currently authorised amount at the time of the call.

### Sequential increment behaviour

The delta is always calculated against the **currently authorised amount** - which only updates when an increment succeeds. After a `failed` or `declined` result, the base stays the same, so the same `amount` value will re-trigger the same outcome on your next attempt.

After a successful increment, the base shifts to the new total. Recalculate before your next test increment to get the outcome you want.

## Get started

- Follow the [Incremental authorisation guide](/docs/guides/merchant/operations/capture-and-settlement/advanced-authorisation/incremental-authorisation) - the sandbox section covers the full delta reference and sequential increment examples
- See the [test cards reference](/docs/guides/merchant/test-and-go-live/testing/test-cards) for available Sandbox payment methods
- See the [API reference](/docs/api/merchant#increment-authorisation) for full request and response schemas