Metrics sent via Datadog HTTP API does not get reflected in Metric Explorer

Referring to Datadog's 'Submit metrics' API documentation, I've tried sending metrics with following payload using Postman:

• API: POST https://api.datadoghq.com/api/v1/series
• Request header: DD-API-KEY and DD-APPLICATION-KEY with valid values
• Request body (based on Datadog sample):

{
    "series": [
        {
            "metric": "IvanPOCMetric",
            "points": [
                [
                    "${NOW}",
                    "1234.5"
                ]
            ]           
        }
    ]
}

The response was successful (202 Accepted) with following response body:

{
    "status": "ok"
}

However, when I try to search for my submitted metrics, via either 'Search metrics' API or Datadog Metric Explorer, I'm unable to find IvanPOCMetric.

Is there any issue with my request payload above? Or is there additional configuration needed to be done on Datadog portal to correctly 'register' the custom metric?

Thanks in advance.