PayPal help please

[Joelsim]

I've set up a PayPal business account and have tried to integrate 'PayPal Express' into my software. When I try to test it I just get a message saying:

'An error received from PayPal Pro Website Payments. Try again or select a different payment method. The error was: Security header is not valid
Please wait for your browser to forward you to the next page or click here'.

My website isn't launched yet and is not yet on it's final URL (that I'm sure I gave PayPal when I set the account up), so I am just testing.

I've checked the details I have put into Business Settings | Payment & Security | Configure Method and they are correct.

Does anyone know what I need to do please? For info I don't have a Pro account with PayPal, just the standard.

Thanks

Joel

[Duncan Rounding]

These KB posts may help initially:

http://community.sellerdeck.com/showthread.php?t=52142
http://community.sellerdeck.com/forumdisplay.php?f=87

[Joelsim]

These KB posts may help initially:

http://community.sellerdeck.com/showthread.php?t=52142
http://community.sellerdeck.com/forumdisplay.php?f=87

Do I need an SSL certificate for Express then?

I just can't work out why it won't go through.

[Duncan Rounding]

PP Pro needs SSL as it collects data on your server but not PP Express as details are entered on the PP servers.