krileon wrote: Ensure you're using a test credit card number that's designed for a successful response. PayPal provides multiple test cad numbers with different test responses. Some will fail payment on purpose.

I don(t know if you are speaking of credit card number of vendor or buyer - so I tried :

Buyer : I see no way to enter a number so I suppose its not this one

Vendor :
I found a page with Test Credit Card Account Numbers and tried to add this one to the buyers account - only I don't know what I have to enter for the cryptogramme. I tried 000 and had a strange error. Then I came back and saw that it was created. I confirmed the card and gave it a try but same error :

FAIL : PDT notification not authenticating at payment gateway

Ok I found my error - I made a confusion between pdt token and merchant id
It works !