Galaxy S7 SM-G930S cannot enable OEM unlock

Hi,

I bought one Galaxy S7 from Korea and would install TWRP, but cannot enable OEM unlock in Settings --> Developer options. Line is inactive.
Can someone help me ?

Android Version
6.0.1
Baseband Version
G930SKSU1APF1
Kernel Version
3.18.14-8382436
dpi@SWHD7516 # 1
Tue Jun 14 11:03:19 KST 2016
Build number
MMB29K.G930SKSU1APF5
SE for Android status
Enforcing
SEPF_SECMOBILE_6.0.1_0013
Tue Jun 14 11:31:51 2016
Security software version
MDF v2.0 Release 7
VPN v1.4 release 6.1
Android security patch level
June 1, 2016

Thanks.

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