samsung edge plus g928f unlocking error.please help

samsung edge plus g928f unlocking error.please help

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hi I have (g928f) 6 edge plus phone. im trying to unlock it but its giving me error. Im also trying to write certi on it but its giving me error there aswel. I have tried on some older version of z3x software but its same thing. please have a look log below..... and please helpppppp
Operation: Unlock
Selected model: SM-G928F
Software version: 23.9
Waiting ADB device... OK
Reading phone info...
Model: SM-G928F
Android version: 5.1.1
Product code: SM-G928FZDAXEU
Phone version: G928FXXU2AOL2
PDA version: G928FXXU2AOL2
CSC version: G928FXEU2AOL1
CSC country code: UK & IRE
CSC sales code: XEU
HW version: MP 0.500
Phone S/N: RF1D45EJGGR
Modem board: SHANNON333
RF cal date: 20150815
IMEI:
Checking Super user right... true
Initializating zTool... OK
Running zTool, please wait... error (7.7.8)
Done with Samsung Tool PRO v.23.9



Operation: Write CERT
Selected model: SM-G928F
Software version: 23.9
Waiting ADB device... OK
Reading phone info...
Model: SM-G928F
Android version: 5.1.1
Product code: SM-G928FZDAXEU
Phone version: G928FXXU2AOL2
PDA version: G928FXXU2AOL2
CSC version: G928FXEU2AOL1
CSC country code: UK & IRE
CSC sales code: XEU
HW version: MP 0.500
Phone S/N: RF1D45EJGGR
Modem board: SHANNON333
RF cal date: 20150815
IMEI:
Checking Super user right... true
Initialization AT RIL... error
Done with Samsung Tool PRO v.23.9