# Create the integration handler

An invoice synchronizer needs to implement the App\Framework\Core\Billing\Invoice\InvoiceSynchronizerHandlerInterface and all of its methods. You have to reference your class inside the install() function in your base class.

Your handler class could look like this:

```php
<?php

namespace custom\modules\HwSevdeskIntegration\Handlers;

use App\Framework\Core\Billing\Invoice\InvoiceSynchronizerHandlerInterface;
use App\Framework\Core\Billing\Invoice\Responses\InvoiceSynchronizerCreatedResponse;
use App\Models\Invoice\Invoice;

class HwSevdeskIntegrationHandler implements InvoiceSynchronizerHandlerInterface {
    public function create(Invoice $invoice): InvoiceSynchronizerCreatedResponse {
    
        // TODO create on remote
    
        return new InvoiceSynchronizerCreatedResponse(
            true, // successfully created
            [ // array of customFields. Save the remote id to refetch the invoice afterwards
                SevdeskHelper::HW_SEVDESK_INVOICE_KEY => $invoiceId
            ]
        );
    }

    public function viewInvoice(Invoice $invoice): ?string {
        
        // TODO fetch pdf from remote
        
        return $pdfContents ?? ""; // return the raw pdf contents
    }
}
```