Facebook Conversions API server-side event returning "The parameter $['data'][0]['event_time'] is required"

Question

When setting up the the Facebook Conversions API I get the following error...

{"error"=>{"message"=>"Invalid parameter", "type"=>"OAuthException", "code"=>100, "error_subcode"=>2804019, "is_transient"=>false, "error_user_title"=>"Server-side API parameter error", "error_user_msg"=>"The parameter $['data'][0]['event_time'] is required.", "fbtrace_id"=>"AaHYqjNBCshoHed-uN2beUP"}}

However I am providing the event_time parameter as requested in the docs.

{
  "data": [{
      "event_name": "ViewContent",
      "action_source": "website",
      "event_source_url": "https://www.mywebsite.com",
      "event_id": 123,
      "event_time": 1666473604,
      "user_data": {
        "client_ip_address": '11.11.11',
        "client_user_agent": 'user-agent'
      }
    }],
    "test_event_code": 'TEST45392'
}