Google Speech to Text API的“无效密钥”

Question

我创建了一个API密钥，并没有对其设置任何限制。但是，在对“语音到文本Api”进行请求时，此代码始终返回“无效密钥”：

import requests
import sys

GOOGLE_SPEECH_URL = 'https://www.google.com/speech-api/v2/recognize?output=json&lang=en-us&key=<real_key>'
f = open("/[....]/file.flac", "rb")
data = f.read()
res = requests.post(GOOGLE_SPEECH_URL, data=data, headers={'Content-type': 'audio/x-flac; rate=16000'})
print(res.text)
f.close()

===>

  <p><b>403.</b> <ins>That’s an error.</ins>
  <p>Your client does not have permission to get URL <code>/speech-api/v2/recognize?output=json&amp;lang=en-us&amp;key=<real_key></code> from this server. Invalid key. <ins>That’s all we know.</ins>

这是怎么回事？