Yesterday I had some issues for paying my fee for a couple of events through the Nets Estonia online web-based terminal. I had entered my card data correctly but after confirmation I got an error:
120 tehing terminalile keelatud
I called Nets first but they did not have technical support available on Sunday and helpdesk saw the error first time. On Monday I tried to pay again and received the same error. I called the merchant this time but they knew nothing about it. Then I called the bank that had issued my card but the payment attempts had not reached them. I called Nets again and this time their technical support handled the case. Comes out that there are multiple types of MasterCard cards and merchant can choose which ones to accept. The type of card that I had was not accepted. This is the first merchant that has not accepted my card.
Hopefully this post helps to debug the issue for someone else too. Unfortunately I have no idea what the message would be in English. Merchants accepting Visa/MasterCard payments through Nets should check their service configuration/contract with the bank/processor whether they can actually receive payments from all cards and won't lose customers.