Security Rules & queries

angular.js

var baseUrl = "https://213das234sdf35dfg.firebaseio.com";

angular.module('starter.controllers', [])
.controller('AppCtrl', function($scope, Auth, $firebaseArray, $firebaseObject) {

  $scope.object = {};
  $scope.projects = [];
  
  Auth.$onAuth(function(authData) {
    if (authData) {
      $scope.authData = authData;

      // This returns the correct data
      var objectRef = new Firebase(baseUrl+"/projects");
      $scope.object = $firebaseObject(objectRef.child("-KBAYwlKln2hf1AmjwwP"));
      console.log("$scope.object:");
      console.log($scope.object);
      
      
      //RETURNS ERROR:
      //permission_denied: Client doesn't have permission to access the desired data.
      var projectsRef = new Firebase(baseUrl).child("projects").orderByChild("team_id").equalTo($scope.authData.auth.slack.team_id);
      $scope.projects = $firebaseArray(projectsRef);
      console.log("$scope.projects");
      console.log($scope.projects);
      
    }
  });
})
.factory("Auth", function($firebaseAuth) {
  var usersRef = new Firebase(baseUrl);
  return $firebaseAuth(usersRef);
});

auth.json

{
  "auth": {
    "uid": "userId1",
    "slack": {
      "url": "https://team1.slack.com/",
      "team_id": "teamId1",
      "user_id": "userId1",
      "team": "team1",
      "user": "name1"
    }
  },
  "expires": 1518207304,
  "token": "BlaBlaFooBArFoObArfOo_sample_token",
  "uid": "userId1",
  "provider": "custom"
}

Data.json

var a = {
  "members" : {
    "userId1" : {
      "team" : "team1",
      "team_id" : "teamId1",
      "url" : "https://team1.slack.com/",
      "user" : "name1",
      "user_id" : "userId1"
    },
    "userId2" : {
      "team" : "team2",
      "team_id" : "teamId2",
      "url" : "https://team2.slack.com/",
      "user" : "name2",
      "user_id" : "userId2"
    }
  },
  "projects" : {
    "-KBAYwlKln2hf1AmjwwP" : {
      "name" : "p1",
      "team_id" : "teamId1"
    },
    "-KBAYyLvBvZ0f47Krf6S" : {
      "name" : "p2",
      "team_id" : "teamId1"
    },
    "-KBA_ohE4tQg3h9gxJPM" : {
      "name" : "asdasd",
      "team_id" : "teamId2"
    },
    "-KBA_p_An2mh7wTdk4iY" : {
      "name" : "asdsa sad",
      "team_id" : "teamId2"
    }
  },
  "teams" : {
    "teamId1" : {
      "team_id" : "teamId1",
      "team_name" : "team1",
      "url" : "https://team1.slack.com/",
    },
    "teamId2" : {
      "team_id" : "teamId2",
      "team_name" : "team2",
      "url" : "https://team2.slack.com/",
    }
  }
};

pure.js

var objectRef = new Firebase(baseUrl).child("projects/-KBAYwlKln2hf1AmjwwP");
objectRef.on('value', function(dataSnapshot) {
  console.log(dataSnapshot.val());
});

//This throws permission_denied errors: Client doesn't have permission to access the desired data.
var projectsRef = new Firebase(baseUrl).child("projects").orderByChild("team_id").equalTo("teamId1");
projectsRef.on('value', function(dataSnapshot) {
  console.log(dataSnapshot.val());
});

SecurityRules.json

{
	"rules": {
	  ".read": false,
	  ".write": false,
		"members": {
		  ".read": false,
			"$id": {
				".read": "auth != null && auth.uid == $id",
				".write": "auth != null && auth.uid == $id"
			}
		},
		"teams": {
		  ".read": false,
			"$id": {
				".read": "auth != null && auth.slack.team_id == $id",
				".write": "auth != null && auth.slack.team_id == $id"
			}
		},
		"projects": {
		  ".read": false,
		  ".indexOn": ["team_id"],
			"$id": {
			  ".read": "auth != null && data.child('team_id').val() == auth.slack.team_id"
			}
		}
	}
}

Finally! Many thanks for helping me understand how to nest rules.
On the official documentation there is no example or text on how to set multiple rules for multiple locations and even here it's just full of copy & paste from those sources!! Thanks again!