$item_data['t3'] = $cycle_units; //cycle units D (days), W (weeks), M (months), Y (years)
$item_data['src'] = '1'; // Recurring payments. If set to 1, the payment will recur unless your customer cancels the subscription before the end of the billing cycle.
$item_data['sra'] = '1'; // Reattempt on failure. If set to 1, and the payment fails, the payment will be reattempted two more times. After the third failure, the subscription will be cancelled.
$item_data['srt'] = ''; // Recurring Times. This is the number of payments which will occur at the regular rate.