app\models\Invoice::getSchedule PHP Method

    public function getSchedule()
    {
        if (!$this->start_date || !$this->is_recurring || !$this->frequency_id) {
            return false;
        }
        $startDate = $this->getOriginal('last_sent_date') ?: $this->getOriginal('start_date');
        $startDate .= ' ' . $this->account->recurring_hour . ':00:00';
        $startDate = $this->account->getDateTime($startDate);
        $endDate = $this->end_date ? $this->account->getDateTime($this->getOriginal('end_date')) : null;
        $timezone = $this->account->getTimezone();
        $rule = $this->getRecurrenceRule();
        $rule = new \Recurr\Rule("{$rule}", $startDate, $endDate, $timezone);
        // Fix for months with less than 31 days
        $transformerConfig = new \Recurr\Transformer\ArrayTransformerConfig();
        $transformerConfig->enableLastDayOfMonthFix();
        $transformer = new \Recurr\Transformer\ArrayTransformer();
        $transformer->setConfig($transformerConfig);
        $dates = $transformer->transform($rule);
        if (count($dates) < 2) {
            return false;
        }
        return $dates;
    }