Google Business Performance API has a NEW API method that allows fetching multiple `DailyMetrics` in a single API request.
Review the deprecation schedule and instructions to migrate over from v4 reportInsights API method to Google Business Profile Performance API.

DailyRange

Time range indicating a date range (both inclusive).

JSON representation 
{
  "startDate": {
    object (Date)
  },
  "endDate": {
    object (Date)
  }
}
Fields
startDate

object (Date)

Required. Inclusive
endDate

object (Date)

Required. Inclusive