Hi Ray, thanks for that advice. I changed it to "_cart" and got an error message from the PayPal payment screen...
We have detected a problem with this shopping cart. If the problem persists, please contact the merchant.
Your purchase couldn't be completed
There's a problem with the merchant's PayPal account. Please try again later.
I changed the PayPal account to my own, which I know is a business account, and added the line you suggested, but this error came up.
Any thoughts you can give me would be really appreciated - I've posted a private link to the latest version of the page