I'm testing the Classifieds plugin with the PayPal Sandbox.

I'm testing the Classifieds plugin with the PayPal Sandbox. I've selected the Sandbox option and used the Sandbox API usernames, password and signature.

When I make a test subscription, I use a Sandbox buyer account. I get this error when I login at sandbox.paypal.com:

The link you have used to enter the PayPal system is invalid. Please review the link and try again.

Am I doing something wrong?