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Installation
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API's
PayPal API
First Step
go to https://developer.paypal.com

Second Step
Login to your account

Third Step
Click the button Create App

Fourth Step
Insert App Name and choose the SandBox Business account, when you finish click Create App

Fifth Step (Live Mode)
Click the button Create App

Sixth Step
Insert App Name then click Create App

When you go back to My Apps & Credentials Page you will find the App that created.
Click on App name and go to app details where you can find the PayPal Client ID and PayPal Client Secret depending on which mode you want (SandBox or Live Mode).