A JSON Schema from https://stackoverflow.com/questions/55225212/use-conditional-statements-on-json-schema-based-on-another-schema-object

schema.json

{
  "$schema": "http://json-schema.org/draft-07/schema#",
  "$ref": "#/definitions/Base",
  "definitions": {
    "Base": {
      "type": "object",
      "additionalProperties": false,
      "properties": {
        "session": {
          "$ref": "#/definitions/Session"
        },
        "sdk": {
          "$ref": "#/definitions/SDK"
        }
      },
      "title": "Base"
    },
    "Session": {
      "type": "object",
      "additionalProperties": false,
      "properties": {
        "start_timestamp": {
          "type": "integer",
          "minimum": 0
        },
        "session_id": {
          "type": "string",
          "if": {
            "SDK": {
              "properties": {
                "name": {
                  "enum": "ios"
                }
              }
            }
          },
          "then": {
            "pattern": "A"
          },
          "else": {
            "pattern": "B"
          }
        }
      },
      "required": [
        "session_id",
        "start_timestamp"
      ],
      "title": "Session"
    },
    "SDK": {
      "type": "object",
      "additionalProperties": false,
      "properties": {
        "version": {
          "type": "string"
        },
        "name": {
          "type": "string",
          "enum": [
            "ios",
            "android"
          ]
        }
      },
      "required": [
        "name",
        "version"
      ],
      "title": "SDK"
    }
  }
}