Hi @DiDA, it is great of you to post such a great APP for non jail broken device. Archive utility doesn't work. After download several software to try, and I've finally found the app for MAC users.
At STEP 6, instead of downloading winrar, please download B1 archiver https://b1.org/download-mac
1. launch B1 and insert the "postknight.imazingapp" file and replace the hack files, and B1 will add a zip file under "postknight.zip"
2. Rename the .zip into .imazingapp, the restore the app as per the step 7 provided by @DiDA
It works well for me. Having 272,009 gems and 2,400,910 coins lvl 7. ha ha ha ha… I'm so happy