Python のエラー

AzureのFaceAPIを利用していますが、初心者ゆえにスクリプトの詳細やエラーの意味がわかりません。サーチしましたが理解することが困難でした。
どなたか解決方法を教えてください。

エラー内容

Traceback (most recent call last):
  File "face.py", line 29, in <module>
    fr = face["faceRectangle"]
TypeError: string indices must be integers

コード

import requests
import matplotlib.pyplot as plt
from PIL import Image
from matplotlib import patches
from io import BytesIO

subscription_key = "＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊＊"
assert subscription_key

face_api_url = 'https://westcentralus.api.cognitive.microsoft.com/face/v1.0/detect'

image_url = 'https://how-old.net/Images/faces2/main007.jpg'

headers = {'Ocp-Apim-Subscription-Key': '＊＊＊＊＊＊＊＊＊＊＊'}
params = {
    'returnFaceId': 'true',
    'returnFaceLandmarks': 'false',
    'returnFaceAttributes': 'age,gender,headPose,smile,facialHair,glasses,' +
    'emotion,hair,makeup,occlusion,accessories,blur,exposure,noise'
}
data = {'url': image_url}
response = requests.post(face_api_url, params=params, headers=headers, json=data)
faces = response.json()

image = Image.open(BytesIO(requests.get(image_url).content))
plt.figure(figsize=(8, 8))
ax = plt.imshow(image, alpha=0.6)
for face in faces:
    fr = face["faceRectangle"]
    fa = face["faceAttributes"]
    origin = (fr["left"], fr["top"])
    p = patches.Rectangle(
        origin, fr["width"], fr["height"], fill=False, linewidth=2, color='b')
    ax.axes.add_patch(p)
    plt.text(origin[0], origin[1], "%s, %d"%(fa["gender"].capitalize(), fa["age"]),
             fontsize=20, weight="bold", va="bottom")
_ = plt.axis("off")