You have defined your schema correctly, except that it doesn't match the data you say you are validating. If you change the property names to match the schema, you still have one issue. If you want to allow "toll" and "message" to be null, you can do the following.

{
  "type": "array",
  "items": {
    "type": "object",
    "properties": {
      "loc": {
        "type": "string"
      },
      "toll": {
        "type": ["string", "null"]
      },
      "message": {
        "type": ["string", "null"]
      }
    },
    "required": [
      "loc"
    ]
  }
}

However, that isn't related to the error message you are getting. That message means that data you are validating is not an array. The example data you posted should not result in this error. Are you running the validator on some data other than what is posted in the question?

"type": "array",
"items": { // this schema applies to all items
  "type": "object",
  "required": [ "address", "first_name", "last_name" ],
  "properties": {
    "address": { "type": "string", ... },
    .. all your other property definitions here...
  },
  "oneOf": [
    { "required": [ "phone_ number" ] },
    { "required": [ "cell_ number" ] }
  ]
}

See https://json-schema.org/understanding-json-schema/reference/combining.html and https://json-schema.org/understanding-json-schema/reference/array.html

Does the second schema correctly identify that "arr is an array of objects that have an integer named type an integer, and either an object named Steps or an object named Heartrate"?

Yes, somewhat. You do not state which properties must exist, and which properties cannot exist together at the same time, which we can do with the "required" and "oneOf" keywords.

Here's an updated schema, and also fixing an error you made in the "Heartrate" section (you said "steps" instead of "heartrates"):

Copy{
  "$schema": "https://json-schema.org/draft/2019-09/schema",
  "type": "object",
  "properties": {
    "arr": {
      "type": "array",
      "items": {
        "type": "object",
        "required": [ "type" ],
        "oneOf": [
           { "required": ["Steps"] },
           { "required": ["HeartRate"] }
        },
        "properties": {
          "type": {
            "type": "integer"
          },
          "Steps": {
            "type": "object",
            "required": ["steps"],
            "properties": {
              "steps": {
                "type": "integer"
              }
            }
          },
          "HeartRate": {
            "type": "object",
            "required": ["heartrates"],
            "properties": {
              "heartrates": {
                "type": "integer"
              }
            }
          }
        }
      }
    }
  }
}

maybe try this:

{
  "type": "array",
  "items": {
    "type": "object",
    "additionalProperties": false,
    "properties": {
      "provider_metadata_id": {
        "type": "number"
      }
    }
  },
  "contains": {
    "type": "object",
    "properties": {
      "provider_metadata_id": {
        "enum": [1, 77, 90]
      }
    }
  }
}

You can achieve this using the anyOf keyword and definitions/$ref to avoid duplication.

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "type": "object",
  "properties": {
    "assetMetadata": {
      "anyOf": [
        { "$ref": "#/definitions/assetMetaData" },
        {
          "type": "array",
          "description": "...",
          "items": { "$ref": "#/definitions/assetMetaData" }
        }
      ]
    }
  },
  "definitions": {
    "assetMetadata": {
      "type": "object",
      "additionalProperties": false,
      "properties": { ... }
    }
  }
}

I got it to work using this validator by nesting the part of the schema for the array elements inside a object with the name items. The schema now has two nested items fields, but that is because one is a keyword in JSONSchema and the other because your JSON actually has a field called items

JSONSchema:

{
   "type":"object",
   "properties":{
      "items":{
         "type":"array",
         "items":{
            "properties":{
               "item_id":{
                  "type":"number"
               },
               "quantity":{
                  "type":"number"
               },
               "price":{
                  "type":"number"
               },
               "title":{
                  "type":"string"
               },
               "description":{
                  "type":"string"
               }
            },
            "required":[
               "item_id",
               "quantity",
               "price",
               "title",
               "description"
            ],
            "additionalProperties":false
         }
      }
   }
}

JSON:

{
   "items":[
      {
         "item_id":1,
         "quantity":3,
         "price":30,
         "title":"item1 new name"
      },
      {
         "item_id":1,
         "quantity":16,
         "price":30,
         "title":"Test Two"
      }
   ]
}

Output with two errors about missing description fields:

[ {
  "level" : "error",
  "schema" : {
    "loadingURI" : "#",
    "pointer" : "/properties/items/items"
  },
  "instance" : {
    "pointer" : "/items/0"
  },
  "domain" : "validation",
  "keyword" : "required",
  "message" : "missing required property(ies)",
  "required" : [ "description", "item_id", "price", "quantity", "title" ],
  "missing" : [ "description" ]
}, {
  "level" : "error",
  "schema" : {
    "loadingURI" : "#",
    "pointer" : "/properties/items/items"
  },
  "instance" : {
    "pointer" : "/items/1"
  },
  "domain" : "validation",
  "keyword" : "required",
  "message" : "missing required property(ies)",
  "required" : [ "description", "item_id", "price", "quantity", "title" ],
  "missing" : [ "description" ]
} ]

Try pasting the above into here to see the same output generated.