Create Flutter Plugin with pod dependencies
I'd a similar problem, with the same output <PBXGroup UUID..., in my case when I ran pod install --verbose I realize that there was an specific error during pod install
undefined method `each_child' for #Dir:0x00007ff10befa7f0 Did you mean? each_slice
Looking for this specific error I found this answer and I realize that I was using ruby 2.5 and one file generated by Flutter for iOS devices was trying to use a method that was introduced on version 2.6.
After follow the steps on that answer I could run my Flutter app on iOS simulator.
The method
dir.each_childwas introduced in Ruby 2.6, but you are using Ruby 2.3.0.
You should update Ruby to 2.6.0 or later 2.x version.
After Ruby updating you may also need to restart your IDE and re-install cocoapods.