G935A Failed to unlock

What can be/ the problem?

Checking Login and Password... OK
Ballance: 15 crd.
You have 15 credit(s) left. This operation takes 5 credits.Continue? Yes
Waiting ADB device... OK
Reading phone info...
Model: SAMSUNG-SM-G935A
Android version: 7.0
Product code: SM-G935AZKAATT
Phone version: G935AUCU4BQD4
PDA version: G935AUCU4BQD4
CSC version: G935AATT4BQD4
CSC country code: USA
CSC sales code: ATT
HW version: REV0.7
Phone SN: R38H40XG9HN
Chip name: MSM8996
Modem board: MSM8996
Security patch: 2017-04-01
RF cal date: 2016.04.28
IMEI: 357216072082192
Waiting for device to become ready... OK
Initialization zTool... OK
Running zTool, please wait...
Start... OK
Initialization... OK
Generate and check client proof... OK
Verify proof by client... OK
Reading data from phone... OK
Searching Ramdump interface... COM9 detected
Reading data from phone... error (3 0)
Done with Samsung Tool PRO v.31.0