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4. Go to admin panel page on your website and add payment method. You will need Client ID and Client Secret from App settings and Merchant ID from Live account settings
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You can find Merchant ID here: https://www.paypal.com/businessmanage/account/aboutBusiness
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5. Result
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6. For testing purposes you can create a couple of sandbox accounts: business and personal. Also create sandbox application instead of live and configure webhook as described above.