Google "exceeded daily limit" issue

I am trying to access the Google Timezone API, but I am getting the following message.

{
   "errorMessage" : "You have exceeded your daily request quota for this API.",
   "status" : "OVER_QUERY_LIMIT"
}

I have enabled my account for billing, and I removed all restrictions from my key. Same issue. This was working fine earlier as it completed over 4700 requests. And my quotas are set...

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What am I missing here?