I am using Appodeals ads integration on Unity LTS 2017.4.40f1 on mac os x Mojave 10.14.5.
The integation fails with error in Unity iOS Resolver window:

Installing CocoaPods...
gem install cocoapods --user-install
WARNING: You don't have /Users/developer/.gem/ruby/2.3.0/bin in your PATH. 
gem executables will not run
ERROR: Error installing cocoapods:
zeitwerk requires Ruby version >= 2.5

Also in unity console I get this error: “Failed to Install CocoaPods for the current user.”

I have tried many things and all failed.

1. I have tried updating my ruby with brew but Unity does not recognize it.
   When I type in terminal: ruby -v
   I get: ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-darwin18]
   Unity still can’t see new Ruby
2. I tried to to install cocoapods manually many times, it worked well but it’s still not recognizable by Unity/Appodeal
3. I tried to go with terminal to Unity project directory and install cocoapods with –user-install switch, and still nothing changed
4. I tried adding Ruby paths to $PATH, nothing changes
5. I tried multiple Ruby versions, including 2.3.0, 2.5.0 and 2.7.0
6. I restarted system and Unity many times, also tried reimporting the plugin
7. Tried multiple solutions from web, nothing works

My question is: how to resolve this problem so Appodeal works on my Unity 2017?
Extra question: why seemingly nothing works, why even with cocoapods installed Unity Appodeal still complains?