当metafield类型为JSON时，Metafield返回错误value：预期Hash为字符串

这个问题可能是由于Metafield API 请求URI中缺少正确的Content-Type标头或使用了错误的Content-Type标头引起的。我们可以通过添加正确的请求标头来解决这个问题，如下所示：

require 'httparty'
require 'json'

# Define your shopify API credentials
api_key = 'YOUR_API_KEY'
password = 'YOUR_PASSWORD'
my_shopify_url = 'https://YOUR_SHOPIFY_STORE.myshopify.com'

# Define your metafield fields
namespace = 'MY_NAMESPACE'
key = 'MY_KEY'
value = {"my_field"=>"my_value"}  # JSON object


# Create a Metafield in shopify using shopify API
response = HTTParty.post(
  "https://#{api_key}:#{password}@#{my_shopify_url}/admin/api/2021-07/metafields.json",
  :body => {
    "metafield": {
      "namespace": namespace,
      "key": key,
      "value": value.to_json,  # Convert the JSON object to a string
      "value_type": "json_string"
    }
  }.to_json,
  :headers => {
    "Content-Type" => "application/json"  # Add the correct request header
  }
)

puts response.body