Screenshots:
Invoice Without Due Date
Invoice With Flat Tax
Invoice Without Tax
Estimate/Quotation
Invoice WIth Payment Method
Custom Invoice Generated From Google Spreadsheet.
About Testing: Tested from android version 7 to 14 with no issues.
AIA File For Testing In Companion:
Invoice.aia (37.3 KB)
For Custom Invoice Design OR Any Document Use This Apps Script Deployed Testing Spreadsheet:
Global Invoice Generator Extension Testing Database - Google Sheets
Extension Size: 24 Kb
This purchase includes AIX & Apps Script.
Price: $5 OR INR 350
More works: 
Bharat Technologies