This works perfectly for me.
1) Boot into TWRP, delete "/data/data/com.google.android.gms/"
2) Boot to System
3) Delete GPay App Data (Cache & Data)
4) Start Gpay Once an close it right now, without adding or changing something
5) Boot into TWRP
6) Note the name of Folder inside "/data/data/com.google.android.gms/app_dg_cache", only one should be here
7) Boot to System
8) Run SafetyNet App, should be green and no errors
9) Boot into TWRP, now there are 2 Folders in "/data/data/com.google.android.gms"
10) delete "/data/data/com.google.android.gms/<FOLDER FROM POINT 6>", the other Folder should stay untouched
11) CHMOD 0551 to folder "/data/data/com.google.android.gms/app_dg_cache"
12) Reboot to System and set up GPay with my Paypal Account