Fix is_manual when marking an invoice as paid

app/Services/Invoice/MarkPaid.php

@@ -56,6 +56,7 @@ class MarkPaid extends AbstractService
         $payment->client_id = $this->invoice->client_id;
         $payment->transaction_reference = ctrans('texts.manual_entry');
         $payment->currency_id = $this->invoice->client->getSetting('currency_id');
+        $payment->is_manual = true;
         /* Create a payment relationship to the invoice entity */
         $payment->save();