PayPal Direct in the UK.. does it actually WORK?

I am trying to set up PayPal Direct (via the API) here in the UK. I have set up a merchant sandbox account, which has a valid email address and API credentials set up, and stored in nopCommerce via the "Configure" link in "Payment Methods" for PayPal Direct. Yet when I try to make a payment to my merchant sandbox account via nopCommerce, it fails with

Payment error: LongMessage: Security header is not valid ShortMessage: Security error ErrorCode: 10002

The API credentials have definitely been set up right, and checking through the code in debug mode I can see that they being passed correctly to PayPal .  What's going on here? Does this type of PayPal payment simply not work in the UK for some reason? Has anybody actually managed to get it to work?

I am using nopCommerce 2.8, running locally on a development machine.

Paypal will be unable to contact your development machine unless you have a fixed IP address/domain.name I think and I doubt your dev IIS will service external requests.

Try uploading the site to an actual domain and set up paypal to respond to that?

Also maybe some of these results will help you?

Ok folks, FYI... I finally got this to work.

The reason it was failing was the IP address field which the PayPal documentation says is recorded for fraud detection purposes. What they don't tell you is that it's validated too. If you try to do a PayPal Direct transaction from a development machine, the IP address that nopCommerce passes to PayPal is "::1" (i.e. a localhost). If you override this in debug mode by pasting in your external IP address, it works.

Thanks Daveb... I was typing my answer at the same time as you were replying, but thanks!