Check Extension Url or Endpoint.
Make sure to review your data:
- Inventory Item Tab → ensure that the Tax Category is set for each item.
- Customer Tab → ensure that all customer details are filled out correctly.
- Sales Invoice / Credit Note Tab → ensure that the following fields are completed:
- Reference
- Customer
- Line Items – Tax Code
- Invoice Sub Type
- Payment Means
- Sales Invoice (Credit Note Form)
- Reason/Note (Credit Note Form)