app/Subscriptions/Plan.php
public function trialDays($trialDays = null)
    {
        if (is_null($trialDays)) {
            return $this->trialDays;
        }

        $this->trialDays = $trialDays;

        return $this;
    }
public function trialDays($trialDays = null)
    {
        if (is_null($trialDays)) {
            return $this->trialDays;
        }

        $this->trialDays = $trialDays;

        return $this;
    }
Specify the number of trial days the plan receives.

@param  int  $days
@return $this