The default cart setup for PayPal only requires the primary email address used at your PayPal account profile setting. If the
Smart Checkout method is used, there must be a
Client ID created. The ID does not exist as a default so it must be done as a process.
Create Client ID
Log into your PayPal account
Go to the developer area at
https://developer.paypal.com/developer/applications
* If an APP already exist, click the name to enter edit mode and get the Client ID
Create a new app to generate the Client ID
- Switch to Live on the top selector
- Click the button labeled Create App to enter the App setup view
- Enter a name in the field labeled App Name to identify if in the list
- Click Create App to save.

Enter a name for the new App

The new App will show the Client ID. Copy the ID.

Paste the copied Client ID into the PayPal Smart Checkout section for Client ID