In order to use PayPal Express Checkout, you need to have a PayPal business account, a standard PayPal account will not work.
Once you have a business account follow these steps:
1. Log into your PayPal account
2. Click the profile icon ( ) on the top right side of the page. From the Business Profile menu, select Profile and Settings.
3. From the left menu, click My selling tools.
4. In the Selling online section, click the Update link for the API access item.
5. To generate the API signature, click Request API Credentials on the API Access page.
6. Select Request API signature and click Agree and Submit to generate the API signature.
The following figure shows this page with an example API signature credential.
7. Login into your SureDone account and navigate to SETTINGS>STOREFRONT.
8. Expand the "Payments" section and set the toggle for "PayPal Express Checkout" to "ON".
9. Insert the details generated from your PayPal account in the below fields.
10. Click Save Settings.