Sandbox error

Hello,

Maybe I’m not getting the concept for sandbox for PayPal Express. I *think* I’ve set it up correctly and I see the word “test” for the account when I login at PayPal using test buyer’s credentials, but then I get this. Please see screenshot. Thanks, Gail

https://snag.gy/9UlTl.jpg

https://www.ads-software.com/plugins/paypal-for-woocommerce/