Google Analytics API: Invalid value at 'report_requests[0].metrics[0]' (expression), Starting an object on a scalar field

Question

Can anyone explain what this means? I'm just trying to grab the pageviews of a specific page.

Here is my request:

{
      path: '/v4/reports:batchGet',
      root: 'https://analyticsreporting.googleapis.com/',
      method: 'POST',
      body: {
        reportRequests: [
          {
            viewId: VIEW_ID,
            dimensions: [{name: 'ga:pagePath' }],
            dimensionFilterClauses: [{filters: [{
                "operator": "EXACT",
                "dimensionName": "ga:pagePath",
                "expressions": ["/about"]
            }]}],
            dateRanges: [{startDate: start,endDate: end}],
            metrics: [{expression: 'ga:pageviews'}]
          }
        ]
      }
    }

Here is the full error:

{
  "error": {
    "code": 400,
    "message": "Invalid value at 'report_requests[0].metrics[0]' (expression), Starting an object on a scalar field",
    "status": "INVALID_ARGUMENT",
    "details": [
      {
        "@type": "type.googleapis.com/google.rpc.BadRequest",
        "fieldViolations": [
          {
            "field": "report_requests[0].metrics[0]",
            "description": "Invalid value at 'report_requests[0].metrics[0]' (expression), Starting an object on a scalar field"
          }
        ]
      }
    ]
  }
}