These templates are created by Government (GSTN). Some offline accounting software like Tally and Busy have options to export data in this format. So if your app uses the same format, you can use these templates to generate the Excel or CSV to be imported to ClearTax. In case of Excel, Government Templates support different segments (B2B, B2CS, etc) in separate sheets of the same workbook and hence can be sent to ClearTax in single request. In case of CSV, each document type (Invoice, CDN, etc) and segment needs to be created as a separate file and sent in a separate request by specifying the data_type and vendor_type as request parameter.