When an invoice being written off (bad debt), the tax amount attached should be deducted also. Current zoho books is the whole written off amount is included tax, it should be separated.

Example, invoice with $100 + $6 tax = $106, payment received $53, overdue $53. Payment haven't received for few months hence written off $53. In such, $50 will go to bad debt $3 will be deducted from "tax payable" at the written off date.