Paypal has two basic genres of payments. Payments Pro, which is the one that deposits money into your paypal account and then you transfer it into your bank, and PayFlow Pro, which deposits directly into your bank account and requires you to get a merchant account separately.
If you use Payments Pro with Express Checkout Only it is free and you can get those credentials from your paypal account. You can log into your paypal account and get those credentials.
Follow these steps:
Log in to your PayPal Business account.
Click the My Account tab.
Click the Profile tab. ...
Click Request API credentials under Account information.
Click Set up PayPal API credentials and permissions under Option 1.
Click Request API Credentials.
Click Request API signature.
Click Agree and Submit.