WHMCS states "Starting with WHMCS 9.0, non-Draft invoices are immutable. This means that you cannot edit transactions on an invoice, and you cannot add items to or remove items from an invoice. "
Unfortunately we sometimes need to fix invoices since WHMCS doesn't allow proper tax handling of products in our area, so we need to be able to fix those invoices.
This happens for example if we add a domain order from the backend where the wrong tax is applied and no hooks exist to reliably fix that.
Requests for proper tax handling exist since years and additional hooks for proper tax calculation on our end exist as well, but haven't been acted upon.
Please don't remove our ability now to manually fix incorrect invoices as well...
Featured Comment
We're pleased to announce that a new Invoice Immutability and Credit Note Control is implemented in WHMCS v9.1.
The default state retains full invoice immutability and credit/debit note functionality to ensure financial compliance out of the box, whilst users who do not require such stringent traceability and audit requirements, can now relax it while keeping billing notes, or turn it off entirely.
This will allow you to work with an invoice to suit your requirements.
For more information check out our release highlights: https://docs.whmcs.com/releases/9-1/9-1-release-highlights/
Try it out yourselves, and share your feedback in the v9.1 Beta Discussion Board: https://whmcs.community/forum/664-whmcs-91-beta-discussion/