[workaround] Clover terminal skipping on-screen signatures but approving payments

[Niksac]

NuGet Package Version

3.4.0

Payment service provider

Telecash

Payment terminal

Clover Flex V3 (C405)

More information

We are using a Clover V3 Flex in Germany via the provider "Telecash".

Most transactions are authorized via on-screen signature, with the signature being submitted and stored at the provider end.

Using the PortalumZVT library (3.4.0) after putting in the card, the terminal immediately jumps back to the "ready" screen without asking for PIN or signature but also omitting the "transaction complete" screen for the customer.
The transaction is reported via ZVT as "successful" to the ECR.
This is a problem as the signature is required in case customers later dispute the payment.

The problem did not occur using alternative ZVT software. There, the customer was asked to sign on-screen with the transaction succeeding afterward.

I compared the TCP traffic when using the different programs and found a workaround which fixes the problem.

The alternative software reports support of the 06 D0 command during registration.
This command is called Menu selection with graphic display and allows the POS terminal to send the image data of a customer signature to the ECR for verification. The ECR will then have to report back to the POS terminal, if the signature looks good and the transaction will progress.

The clover terminal will never actually use that command but only behaves correctly, if the ZVT Client reported support for it.

For our use-case, I implemented a registration option which allows to "fake" support for 06 D0.
This fixes all problems for us.

I don't think this is a proper solution to be incorporated into the library. I cannot properly implement and test the command with the terminal I have not actually using it.

I created this issue in case other people have the same problem and want to try the workaround.
It can be closed immediately.

[kaplanerkan]

You need to test it yourself, becau i dont have this model and device:

The root cause is that the ECR needs to declare support for the 06 D0 command (Menu selection with graphic display) during registration. Clover
terminals check this capability before enabling signature capture.

Current Implementation (ZvtClient.cs)

The registration currently only declares support for 06 D1 (Print Line) and 06 D3 (Print Text Block) in TLV Tag 26:

// Tag 26 - List of permitted ZVT commands
tlvContainer.Add(0x26);
tlvContainer.Add(0x08); // length = 8 bytes (2 commands)
// 06 D1 - Print Line
// 06 D3 - Print Text Block

Solution

Add 06 D0 to the Tag 26 command list:

// Tag 26 - List of permitted ZVT commands (06 D0, 06 D1, 06 D3)
tlvContainer.Add(0x26);
tlvContainer.Add(0x0C); // length = 12 bytes (3 commands)

// 06 D0 - Menu selection with graphic display (enables signature)
tlvContainer.Add(0x0A); // ZVT-command indicator
tlvContainer.Add(0x02); // length
tlvContainer.Add(0x06);
tlvContainer.Add(0xD0);

// 06 D1 - Print Line
tlvContainer.Add(0x0A);
tlvContainer.Add(0x02);
tlvContainer.Add(0x06);
tlvContainer.Add(0xD1);

// 06 D3 - Print Text Block
tlvContainer.Add(0x0A);
tlvContainer.Add(0x02);
tlvContainer.Add(0x06);
tlvContainer.Add(0xD3);

This tells the terminal that the ECR supports graphic display/signature capture, even if the actual 06 D0 response handler isn't fully implemented.
 The terminal will then enable the signature workflow.

[Niksac]

Yes, your approach is similar to what i did on my branch.
It solves our problem.
Just posted this for others to find.

If we ever switch to a device which actually uses 06 D0 i will try implementing it for real.