I have a request from a German customer regarding GOBD compliancy regarding invoices in Zoho CRM.

He wants me to secure, that an invoice cannot be updated or deleted, as soon as the invoice has a certain status e.g. "Approved" or "Final".

This is a requirement for invoice documents to make sure, that a invoice, which is once delivered to customer cannot be changed later on.

The only way would be to create a storno - Credit Note - for the old invoice and the create a new invoice.