[Samsung Galaxy S7 Questions and Answers] yhn:
As we all know, Samsung Pay doesn't work with rooted devices, even with fake Knox 0x0 or MagiskHide. Some people where saying that MagiskHide doesn't work with SPay because of the "Custom" system status, but even with ROMs that fake the Official status, the app doesn't work.

I was investigating about it on my phone, messing around with MagiskHide and SPay to see if I could get something to work and, later I noticed a file called com.samsung.android.spay.log in the root directory. Upon investiganting the file, I've encourted the following entries (I only copied the first sections because the file is too long)

<Information>
com.samsung.android.spay
/data/app/com.samsung.android.spay-1/base.apk
/data/app/com.samsung.android.spay-1/lib/arm
/data/user/0/com.samsung.android.spay
866531105e5d7f5c
arm64-v8a/armeabi-v7a
SM-G930F
24
</Information>

<Detection>
Date Time Source Policy Summary Current Warning Ver Name Description
2018-02-08 13:37:02 [6042] 52355100 00004000 00004000 00004000 4.4.3 (ROOTED ) MAGISK
2018-02-08 13:37:02 [6043] 52355100 00006000 00002000 4.4.3 (ROOTABLE ) MAGISK
2018-02-08 13:37:02 [6041] 52355100 02006000 02000000 02000000 4.4.3 (RSH ) MAGISK
2018-02-08 13:37:06 [3120] 52355100 03006000 01000000 4.4.3 (MIRRORING ) com.sec.android.sidesync30
2018-02-08 14:16:33 [1302] 52355100 03006800 00000800 4.4.3 (USBDEBUG ) USB Plugged
2018-02-08 14:42:54 [6042] 52355100 00004000 00004000 00004000 4.4.3 (ROOTED ) MAGISK
2018-02-08 14:42:54 [6043] 52355100 00006000 00002000 4.4.3 (ROOTABLE ) MAGISK
2018-02-08 14:42:54 [6041] 52355100 02006000 02000000 02000000 4.4.3 (RSH ) MAGISK
2018-02-08 14:46:36 [6042] 52355100 00004000 00004000 00004000 4.4.3 (ROOTED ) MAGISK
2018-02-08 14:46:36 [6043] 52355100 00006000 00002000 4.4.3 (ROOTABLE ) MAGISK
2018-02-08 14:46:36 [6041] 52355100 02006000 02000000 02000000 4.4.3 (RSH ) MAGISK
2018-02-08 15:02:19 [6042] 52355100 00004000 00004000 00004000 4.4.3 (ROOTED ) MAGISK
2018-02-08 15:02:19 [6043] 52355100 00006000 00002000 4.4.3 (ROOTABLE ) MAGISK
2018-02-08 15:02:19 [6041] 52355100 02006000 02000000 02000000 4.4.3 (RSH ) MAGISK
2018-02-08 15:15:21 [6042] 52355100 00004000 00004000 00004000 4.4.3 (ROOTED ) MAGISK
2018-02-08 15:15:21 [6043] 52355100 00006000 00002000 4.4.3 (ROOTABLE ) MAGISK
2018-02-08 15:15:21 [6041] 52355100 02006000 02000000 02000000 4.4.3 (RSH ) MAGISK
2018-02-08 15:15:47 [6042] 52355100 00004000 00004000 00004000 4.4.3 (ROOTED ) MAGISK
2018-02-08 15:15:47 [6043] 52355100 00006000 00002000 4.4.3 (ROOTABLE ) MAGISK
2018-02-08 15:15:47 [6041] 52355100 02006000 02000000 02000000 4.4.3 (RSH ) MAGISK
2018-02-08 15:15:50 [3120] 52355100 03006000 01000000 4.4.3 (MIRRORING ) com.sec.android.sidesync30
2018-02-08 15:19:38 [6042] 52355100 00004000 00004000 00004000 4.4.3 (ROOTED ) MAGISK
2018-02-08 15:19:38 [6043] 52355100 00006000 00002000 4.4.3 (ROOTABLE ) MAGISK
2018-02-08 15:19:38 [6041] 52355100 02006000 02000000 02000000 4.4.3 (RSH ) MAGISK
</Detection>

<Processes>
Pid Uid PPid ProcessName
16723 10056 16689 mngreq
16689 10056 3422 com.samsung.android.spay
</Processes>

And that's why SPay don't work on rooted devices, is because it can still detect Magisk with MagiskHide enabled, and not because of Knox 0x0 or "Custom" system status.

TL;DR - MagiskHide doesn't work with SPay. But if we can make it to, then theoretically we will be able to have Samsung Pay working on rooted and Knox 0x1 phones.