code: public function save()
      {
          if (!$this->response) {
              throw new Exception('No activation response was recieved.');
          }
  
          // Get the plan charge
          $planCharge = $this->shop->planCharge();
  
          // Create the charge
          $charge = new Charge();
          $charge->type = Charge::CHARGE_USAGE;
          $charge->reference_charge = $planCharge->charge_id;
          $charge->shop_id = $this->shop->id;
          $charge->charge_id = $this->response->id;
          $charge->price = $this->response->price;
          $charge->description = $this->response->description;
          $charge->billing_on = $this->response->billing_on;
  
          return $charge->save();
      }
docs: Saves the usage charge to the database.
  
  @return bool