Filter the payTypeIdentifier sent to Specter

wc-specter-pay-type-identifier.php

/**
 * Specter for WooCommerce
 * Filter the payTypeIdentifier sent to Specter
 *
 **/

add_filter('wc_specter_pay_type_identifier', 'my_wc_specter_pay_type_identifier', 10, 2);

function my_wc_specter_pay_type_identifier( $paytype, $order_id ) {
	// Switches the paytype to D (cash payment) for all orders that uses Cach on Delivery (originally paytype P in the extension) as the payment method.
	// See available paytypes here: http://docs.krokedil.com/se/documentation/specter-woocommerce/#10
	
	if( 'P' == $paytype ) {
		return 'D';
	} else {
		return $paytype;
	}
}

Do change the paytype for a specific payment method you could do something like this:

function my_wc_specter_pay_type_identifier( $paytype, $order_id ) {
$order = wc_get_order( $order_id );
	if ( 'payson' === $order->get_payment_method() ) {
		$paytype = 'PCO';
	}
	return $paytype;
}