added adyen payments documentation

docs/2-BFF/06-practical-task-4-checkout.md

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+---
+sidebar_position: 7
+---
+
+# 2.6. Practical Task - Implement Adyen Checkout
+
+## What is this task about
+
+This task is aimed at developing server-side logic for a checkout flow in a store running on the Magento platform. Your role will be to develop a server-side component whose task is to place an order.
+
+## What should be done
+
+You need to implement a  Adyen checkout-session that will be used on the StoreFront side.
+
+- Creating session that managed by Adyen
+- Storefront should use your BFF API to proceed payment
+
+#### Create Adyen account
+To start proceeding payments - create your own test Adyen account.
+Registration: https://www.adyen.com/signup
+
+![Adyen SignUp](assets/2.8/adyen-signup.png)
+
+You can use fake data for it, temporary email and phone number.
+
+#### Adyen keys
+TO be able to create the sessions and proceed payments, you should generate some keys for app to identify you.
+Go to Developers tab/API credentials and select your account.
+
+![Api-Credentials](assets/2.8/api-creds.png)
+
+On the next page you should generate some keys and make a white list with your hosts. Save your keys somewhere.
+
+![Api-key](assets/2.8/api-key.png)
+
+Then generate the client-key, it will be used on the Front-End side. Also you should add the host you're going to use to the white list, to avoid CORS errors.
+
+![client-key-and-hosts](assets/2.8/client-key.jpg)
+
+Make sure you are using the latest version of the Front-End App. Create ".env" file and paste your client-key there in the following way:
+`ADYEN_CLIENT_KEY="test_..."`
+
+Also, you'll need merchant account for your session request. So your merchant account is - `{YOUR_COMPANY_NAME}ECOM.`
+
+## Task
+
+1. Create API endpoint `POST /chckout?amount={amount}` for the payment session
+Session flow example: https://docs.adyen.com/online-payments/tokenization/sessions-flow/?programming_language=ts