🐛 Fix financial doc

[jonathanMindee]

PR Details

Fix for FinancialDocument API

Description

The Invoice version used for FinanicialDocument was "v1" and it led to errors.
The tax rate can now be None with the V2, fixed this error.

How Has This Been Tested

Fully tested

Types of changes

• [ x] Docs change / refactoring / dependency upgrade
• [x ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• [ x] My code follows the code style of this project.
• [ x] I have added tests to cover my changes.
• [x ] All new and existing tests passed.