Paypal Sandbox Testing

Hello

I just need a little guidance on how to set up sandbox testing for Paypal.

What’s the best way to do this? What website should I use? Is it developer.paypal.com?

I’ve tried setting up a sandbox account on developer.paypal.com, but when it comes to testing I get the following error :

Unable to find token
(url https://www.sandbox.paypal.com/webscr&cmd=_express-checkout&token=)

Am I doing this right, or is it different for non US developers?

Thanks

Tim