@Leonorleans You're welcome, hope it will work.
Another thing you can try, that I can think of if it still doesn't work:
Go to the Google Play Store and tap the three lines in your upper left corner. You will see there an section called "Play Protect". Tap on that, and you will see an option "Scan device for security threats", you should turn that off.
Also, go to your phone Settings - > Additional Settings - > Privacy, and turn on the option "Unknown sources". Then try to install that mod again.
@iambellie I can't help you with that facebook issue, since I didn't connect my facebook to the game. I had that same issue, but it didn't bother me much, because I didn't have much of a progress before that. I think I've read somewhere that, if you are having that issue, you need to delete the Facebook app (if you have it installed), but I can't remember, try searching this forum, I believe I've seen a lot of people having trouble connecting to facebook.
And yes, MOD has only unlimited diamonds, not keys, which is a bummer. :/ But I guess you can't have everything, i am grateful for these free premium choices as well.