In this article I am going to explain how you can integrate PayPal express checkout with Asp .Net Core using REST API to process payments.
1- Download the sample project
I have created an Asp.net core project using VS 2017 for you. You can download it from Github https://github.com/rizksobhi/PaypalExpressCheckout
2- Create a PayPal App
Go to PayPal developer , and under REST API apps click Create App
3- Update ClientID and Client Secret
Copy the ClientID and Secret from Sandbox and update appsettings.json in the PayPalExpressCheckout.Web application
4- Update Payee and Payer information
Go to PayPalServices and update the Payee email and merchant_id
For testing purposes, PayPal provides testing accounts that you can create under your PayPal account. You can create test buyer and seller accounts from Sandbox environment for testing
To create test accounts, go to Sandbox -> Accounts and click on Create Account and follow the instructions
6- Build and Run the solution. YOU ARE ALL SET.
Rizk Hanna 
Cool job man. Thanks.
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How to get merchant_id ?
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You should be able to find it at the payee PayPal account
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I am having some trouble getting the app to start. The Index view fails to show at all.
Could you please provide some insight as to why this may be happening.
I am using VS 2017. I have followed your instructions exactly.
All changes with respect to payee and merchant have been completed.
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what error do you see? you could use the VS diagnostic tools to spot the error!
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