> For the complete documentation index, see [llms.txt](https://docs.rocketfuel.inc/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.rocketfuel.inc/integrations/rocketfuel-integration/how-to-guide/using-the-rocketfuel-api-for-custom-integration.md).

# Using the RocketFuel API for Custom Integration

RocketFuel has three phases of API integration:

1. Pre-Payment Activity
2. Payment Activity (Shopper ↔︎ RKFL)
3. Post-Payment Activity

Before the start of the three phases, some prerequisites are required to be completed. The below Quick Start page describes on the same.

{% embed url="<https://docs.rocketfuelblockchain.com/developer-guides/quick-start>" %}

Once the `public key` and `integration keys` have been set up, the first phase can be started.

1. **Pre-payment Activity**
   1. To start with the prepayment activity, there is one more prerequisite that needs to be understood - [Encryption Algorithm](https://docs.rocketfuelblockchain.com/developer-guides/api-reference/encryption-algorithm)
   2. After the above things are completed and understood, the first phase starts with [generating the invoice](https://docs.rocketfuel.inc/developer-guides/api-reference/generate-invoice-link).&#x20;

      i. The [inline method](https://bitbucket.org/rocketfuelblockchain/rocketfuel-readme/src/master/javascript-sdk.md) can be used as well for generating invoice
2. **Payment Activity (Shopper ↔︎ RKFL)**

   The second phase, payment activity involves the exchange of data between shoppers and RocketFuel, nothing is expected from the merchants.
3. &#x20;**Post Payment Activity**\
   The post payment activity involves knowing the transaction status which can be done with the help of webhooks and Lookup API.
   1. [Webhook](https://docs.rocketfuel.inc/webhooks)
   2. [Lookup API](https://docs.rocketfuel.inc/developer-guides/api-reference/transaction-lookup)

**Languages Supported**

1. Any coding language to call APIs (server ↔︎ server)
2. Little knowledge of JS in case of Inline /popup Integration


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