In order to use PayPal Express Checkout you need to have a business account, a standard paypal account will not work.
Once you get a business account, follow these steps and that will fix the issue.
Log into your paypal account and follow these instrcutions:
1, First, log in to your Paypal account
2, Click "My Profile" under the "My Account" tab.
3, Find "My selling tools"
4, Find and click on "API access" (see image 1)
5, Find and click on "Enable Express Checkout" (see image 2)
6, Make sure you select "Accept Paypal payments before API permissions are set up" (see image 3)
7, Make sure you click the Submit button to save the setting
8, You should now return to your Paypal profile with a message saying that your preferences have been saved.