> For the complete documentation index, see [llms.txt](https://integration-guide.redeem.gov.sg/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://integration-guide.redeem.gov.sg/phase2-integration/api-documentation/redeeming-a-qr-code-voucher/making-idempotent-redemption-requests/introduction.md).

# Introduction

### 4.2.1 Introduction

For example, if the request to redeem a voucher does not respond due to a connection issue, you can retry the request with the same idempotency key sent in the first request to guarantee that no more than one voucher redemption operation is attempted.

This is **important** as vouchers cannot be logically redeemed twice. Subsequent attempts without idempotency key header to redeem the same voucher will **always** result in a <mark style="color:red;">`HTTP 402`</mark> response with error code, <mark style="color:red;">`redemption_vouchers_used`</mark>, as the voucher has already been redeemed in the prior request.

If subsequent retries are not identified with an idempotency key, disputes on whether the vouchers were successfully redeemed or was already used could occur.

{% hint style="info" %}
It is compulsory for retailers to include idempotency key whenever making a redemption call to RedeemSG API
{% endhint %}


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