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@Action Hank
Ok, I fixed the problem with Wi-Fi Calling
@balrog20 @Kill-Switch
Android 8 have completely different files structure in CSC folder than Android 9. So, patching by CSCSelection_V3.0.0 created for Oreo won't give you Wi-Fi calling, but will only make a mess in files.
In the attachment there is a zip archive for working VoLTE and Wi-Fi calling for Poland XEO and Orange operator. All you have to do is open this rom file (BlackDiamond.NFE.PIE.V2.0.zip) by win-rar, go to /System/csc, delete everything from this folder and put there files from attachment. Next, do full wipe from recovery and flash phone using modified rom file.