If you test your PayPal Business integration with the same or another Business account, there might be a problem. PayPal forbids payments between two Business accounts.
Check your PayPal payment's URL. If it is "sandbox.paypal.com," you are attempting to complete the payment from the PayPal sandbox. It can be tested with Sandbox accounts only. Learn more about creating sandbox accounts from the PayPal guide.
If you see "code=EWP_SETTINGS" in the URL of the PayPal error page, you need to allow unencrypted websites to make payments to PayPal. To do so, log in to your PayPal account, click on Profile → Selling Preferences → Website Payment Preferences. Scroll down to the "Encrypted Website Payments" section and select "Off" next to "Block Non-encrypted Website Payment."