How to Build a Crypto Payment Gateway with Swaps

It looks like you're building a payment verification system for cryptocurrency transactions, specifically focusing on handling swaps and settlements. Here's an overview of the steps involved in creating such a system based on your provided code snippets:

Step-by-Step Guide

1. Get Payment Quote

   • This function fetches details about the swap transaction from an external API (e.g., SwapRabbit).
   • It includes parameters like chainId, tokenIn (the token being swapped), amount, and sender.

2. Format Settlement Amounts

   • The formatSettlement function converts raw settlement amounts into human-readable formats based on the number of decimals for the settlement token.

3. Server-Side API Endpoint (POST /get-payment-quote)

   • This endpoint handles incoming requests from your frontend to get a payment quote.
   • It stores the quote in memory (or Redis/database) with an expiry time, typically 30 seconds.
   • Returns details like orderId, settlement amounts, price impact, and transaction data.

4. Verify Payment Execution

   • After the customer submits the swap transaction, your backend needs to verify if it was successful.
   • This involves checking if the

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