add_action( 'added_post_meta', 'sliced_woocommerce_set_subscription_terms', 10, 4 );
function sliced_woocommerce_set_subscription_terms( $meta_id, $post_id, $meta_key, $meta_value  ) {

	if ( $meta_key !== '_sliced_invoice_woocommerce_order' ) {
		return;
	}

	// this is your woocommerce order number... use it to get any details you need from the order
	$order_number = $meta_value;

	// add your subscription details here... here's a list of all the possible ones, use only what you need
	$subscription_meta = array(

		// status - this is important, must be either "pending" (customer still needs to submit credit card info and start subscription), "active" (customer has already started subscription), or "cancelled".
		'_sliced_subscription_status'                => 'pending',

		// amount - this is the recurring amount fully formatted, including currency symbol (ex. $115.00)
		'_sliced_subscription_amount'                => sliced_get_invoice_total( $post_id ),

		// amount_raw — this is the recurring amount numbers only (ex. 115)
		'_sliced_subscription_amount_raw'            => sliced_get_invoice_total_raw( $post_id ),

		// interval_number — any number. For example, if the subscription is to charge once every month for 6 months, you would enter 1 here and "months" for interval_type
		'_sliced_subscription_interval_number'       => 1,

		// interval_type — can be "days", "months", or "years"
		'_sliced_subscription_interval_type'         => "months",

		// cycles_count — only if above is "fixed", then enter the number of cycles here.  otherwise leave blank.  For example, if the subscription is to charge once every month for 6 months, you would enter 6 here.
		'_sliced_subscription_cycles_count'          => 6,

		// cycles_type — can be either "fixed" (a set number of charges), or "infinite" (charge until cancelled)
		'_sliced_subscription_cycles_type'           => "fixed",

		// trial — if you want a trial period, put 1 here.  otherwise leave blank.
		'_sliced_subscription_trial'                 => 1,

		// trial_interval_number — any number
		'_sliced_subscription_trial_interval_number' => 7,

		// trial_interval_type — "days", "months", or "years"
		'_sliced_subscription_trial_interval_type'   => "days",

		// trial_cycles_count — any number
		'_sliced_subscription_trial_cycles_count'    => 1,

		// trial_amount — any amount
		'_sliced_subscription_trial_amount'          => 0,

		// receipts — put 1 if you want receipt invoices to be created for each successive payment, otherwise blank
		'_sliced_subscription_receipts'              => 1,

		// receipts_auto_send — can be either "yes" or "no".
		'_sliced_subscription_receipts_auto_send'    => "yes",

		// braintree_plan - required only if planning to use Braintree for payments
		'_sliced_subscription_braintree_plan'        => "xyzzy123",

	);

	foreach ( $subscription_meta as $key => $value ) {
		update_post_meta( $post_id, $key, $value );
	}

}