Paypal error in Directory Plugin

I’m still setting up the directory plugin. During the checkout process when the paynet should be sent to Paypal) I get to see this error message:

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

I’ve entered my API credentials in the admin area. i got them from Paypal under “Option 2 –

This option applies to:

*Custom websites and online stores

*Pre-integrated shopping carts running on your own server.

Underneath that option there’s this message:

“Accept payments from your online stores before setting up APIs

Enable Express Checkout to accept payments from your online stores right away. You can set up API permissions or credentials later.”

Do I perhaps need to enable this for the script payments to work?