As said in the title, we are trying to catch when a customer cancels an appointment to refund him what he paid. We saw that when a apointment is cancelled it makes a call to "admin-ajax.php?action=wpamelia_api&call=/bookings/cancel/id&source=cabinet-customer".

Is there any way to catch when that is called and make woocommerce refund to the customer?

Hello,

We managed to add this feature for customers. Just need to add this code to admin-ajax.php:

if($_GET['action'] == "wpamelia_api" && $_GET['source']=="cabinet-customer"){
    global $wpdb;
    $call = explode("/",$_GET['call']);
    if($call[1]=="bookings" && $call[2]=="cancel"){
        $appointmentID = $call[3];
        $payment = $wpdb->get_results("SELECT p.customerBookingId,p.wcOrderId,p.amount FROM {$wpdb->prefix}amelia_payments p WHERE p.customerBookingId = ". $appointmentID."")[0];
        $order  = wc_get_order( $payment->wcOrderId );
        $order_items   = $order->get_items();
        $line_items = array();
        if ( $order_items ) {
            foreach( $order_items as $item_id => $item ) {
                $item_meta  = $order->get_item_meta( $item_id );
                            $tax_data = $item_meta['_line_tax_data'];
                $refund_tax = 0;
                        if( is_array( $tax_data[0] ) ) {
                            $refund_tax = array_map( 'wc_format_decimal', $tax_data[0] );
                        }
                        $refund_amount = wc_format_decimal( $refund_amount ) + wc_format_decimal( $item_meta['_line_total'][0] );
                        $line_items[ $item_id ] = array(                     'qty' => $item_meta['_qty'][0],                     'refund_total' => wc_format_decimal( $item_meta['_line_total'][0] ),                     'refund_tax' =>  $refund_tax );
            }
        }
        $refund = wc_create_refund( array(
            'amount'         => $payment->amount, // you can modify the amout if you want to add a tax or smth
            'reason'         => "reason here",
            'order_id'       => $payment->wcOrderId,
            'line_items'     => $line_items,
            'refund_payment' => true
        ));
    }
}