Error using PayPal WPP with sandbox

I'm a complete newbie, getting a local test site working as a dry run before going for a live one. I'm using the paypal sandbox to test the payment methods.

I've got Paypal Express Checkout working fine, so I'm sure I've got all the API details right. Using Website Payments Pro, though, when I put a test VISA transaction through, I get a big red error:

"We were not able to process your order. Please select an alternate payment method, or contact the store owner for assistance."

I'm wondering if this might be related to the Cardinal Centinel settings, which I left at their default values as I don't know what to put in them. I've now figured out it's related to 3D Secure and submitted my Cardinal registration, so hopefully I should be able to get that set up soon, but anyway this is a VISA transaction and from what I've read 3D Secure is only mandatory for Maestro. Besides, going through Paypal Express Checkout with this fake card worked, without any 3D Secure page appearing. I'm not sure if 3D Secure would even work with the paypal sandbox.

I had enabled Debug Logging to email and file. There wasn't anything that looked like an error in the log file, but I did receive a couple of emails like the following (not sure if it was from the logging or a more general alert):

ALERT: PayPal Direct Payment Error

Customer arrived on the order process page without attempting authentication
lookup.

Problem occurred while customer 1 Tom Bowles was attempting checkout with
3D-Secure authentication.paypaldp

Many thanks for any help,
Tom
(Using 1.3.9h, only add-in is EasyPopulate)

You can't test WPP and Cardinal in sandbox. You'll need to go live to test that.

OK, guess I'll have to test with a real account and small payments.

Thanks for the help,
Tom

I've switched to live and got Cardinal working, and that appears to have removed that error. However, now I'm getting emails like the following, accompanied by the same big red error:

ALERT: PayPal Direct Payment Error ( 26 [Invalid vendor account])

We were not able to process your order. Please select an alternate payment method, or contact the store owner for assistance. ( 26 [Invalid vendor account]) Invalid vendor account -

Express checkout works (with 3D secure and a live credit card and paypal merchant account).

Website Payments Pro is activated and showing as live on the paypal site ("Account status: Verified" and "Application status: Approved" on the Overview page, and "Website Payments Pro - Live" on the Profile page).

I have entered the API username, password and signature correctly. I'm pretty sure of this because I have tested them by using them to connect to the PayPal NVP API from a script and execute a transaction search.

Most references I can find to this error appear to be talking about PayFlow, which is odd. The various FAQs and forum responses talk about setting the "vendor", "partner", etc correctly. I'm not using payflow, and don't intend to. I don't have a Payflow account. Payflow isn't required for WPP to work with Zen Cart, is it?

Under the Express Checkout module's options, I am selecting "Paypal Mode" as just "Paypal".

Sorry to post to the forum twice in as many days, but I've experimented, hunted around and bought the book, and I really am stumped here.

Again, many thanks for any help
Tom

OK, I figured it out. At https://www.zen-cart.com/tutorials/index.php?article=28, it says

In the UK, the Payflow Pro service is actually bundled as a hybrid service with Website Payments Pro, connecting all the transactions to your UK PayPal account, and all monies are deposited to your PayPal account, instead of directly to your bank account.

So yes, WPP in the UK requires (or in some sense is) payflow.

I generated some PayFlow credentials by going to "Request API Credentials" in my business account on the paypal site, going for option 2 - "Payflow Pro" and "Set up Payflow Pro API Access". This gave me values for the 4 fields, which I entered into the settings under the paypal express checkout module after setting the "Paypal Mode" field to "Payflow-UK". It actually didn't work at first (giving the same error as before), but one of the following two things sorted it out:

• Generating a second set of payflow credentials and using those instead of the first ones
• Going to the Website Payments Pro module in zen cart, and clicking edit and save

Or perhaps I'd simply mis-copied the first lot of credentials and got it right the second time. Just listing those on the off-chance it might help someone else in the same situation. Anyway, sorted!

Right.
See: http://www.zen-cart.com/index.php?main_page=page&id=29