type MyStruct struct {
  ID    int                    "json:'id'"
  Value map[string]interface{} "json:'value'"
}

func handler(ctx *fiber.Ctx) {

  requestData := []MyStruct{}
  if err := ctx.BodyParser(&requestData); err != nil {
    log.Fatal(err)
  }
  //*************************************************************************
  rowsToinsert := [][]interface{}{}
  for _, item := range requestData {
    rowsToinsert = append(rowsToinsert, []interface{}{item.ID, item.Value})
  }
  //*************************************************************************
  tableName := pgx.Identifier{"mytable"}
  columnsToUpdate := []string{"id", "value"}
  tcontext, _ := context.WithTimeout(context.Background(), time.Second*5)
  _, err := db.Pool.CopyFrom(tcontext, tableName, columnsToUpdate, pgx.CopyFromRows(rowsToinsert))
  //.....
}

go get -d golang.org/x/website/    
can't load package: package golang.org/x/website: no Go files in /Users/user/go/src/golang.org/x/website

go get -d golang.org/x/website