Hello, @JelenaS ,
If an Invoice is not yet posted (Invoice Status = Hold, Balanced, Pending Approval, Pending Print, Pending Email, Credit Hold, Scheduled or Rejected) changes can be made as needed. Invoices may contain positive and negative lines, but may not be Negative in Total. If an Invoice is Negative in Total, it’s a Credit Memo document type, not an Invoice.
Because Acumatica is a GAAP compliant (Link) accounting system, Acumatica does not allow changes to Posted Documents. To search Product Ideas, Go to Product Ideas (link) section of Acumatica Community and use Search field at the top.
(I searched Product Ideas for “Change Posted Invoices” and did not see any suggestion that will allow changes/additions to posted invoices.)
I know Notes and Attachments may be added to posted documents. Description field of related documents may be used to relate documents to each other. Global Search at the top of any Acumatica browser tab can search system-wide across all modules and screens, such as for a reference number or customer. For example, when entering “10501” to search for Invoice 10501, Acumatica’s Global Search will find not only Invoice 10501 but will also find all documents that had 10501 typed into the Description Field.
Reports like Customer Balance and Vendor Balance, when printed for all documents in the current period, or for All Documents, will also display all documents for your customer/vendor in one place.
I hope I have answered your question.