fix

alkatorapi/models.py

@@ -138,6 +138,9 @@ class InvoiceProduct(models.Model):
         if data['quantity'] <= 0:
             raise ValidationError("Počet předmětů ve faktuře musí být kladný!")
 
+    def __str__(self):
+        return f"<InvoiceProduct {self.product.name} {self.invoice.invoice_id} *{self.quantity}"
+
 
 class Racer(InvoiceProduct):
     profile = models.ForeignKey(Profile, related_name='racers', on_delete=models.RESTRICT)

alkatorapi/views.py

@@ -138,7 +138,6 @@ def register_racer(request):
     )
     invoice.save()
     racer.save()
-    invoice.items.set([racer.id])
 
     payment_data = {
         'merchant': COMGATE_MERCHANT,