Fix invoice data improvement - Apply to existing invoices
This one is very easy and incredibly useful.
WHMCS has an official "fixed invoice data" mod. In the Euro zone, invoices need to be sequential, can't be modified, etc.
This mod only applies to invoices issued AFTER you install it. Customers are still able to edit old invoices simply by changing their company details.
Also, simple mistakes like typos can't ever be corrected.
Add a "fix data" button to the invoices.
The "fix data" button will read the current info in the Profile and lock it into the invoice. So, in case of a typo, you can just correct the profile and hit "update" for the affected invoices.
A mass update of old invoices should be provided, so the ones created before the mod can have fixed data as well.
Why it's easy:
You already have the code for serializing the invoice data. All we need is a way to run it on individual invoices, or a list of invoices.