What is the problem?
When exporting sales or purchase invoices you need to include the VAT number of your customers or suppliers.
How to solve
Sales invoices
Go to Analytics>Reports
Click on Sales
Select Book Invoices Issued on the left sidebar
Filter by the date range you require
Click on the Download icon at the top right and choose either PDF or Excel
Purchase Invoices
Go to Analytics>Reports
Click on Purchases
Select Invoices Received Book in the left sidebar
Filter by the date range you require
Click on the Download icon at the top right and choose either PDF or Excel