Unfortunately, redacting an invoice has to be done following rules and the Accounting Law. There are some “industry” practices that your accountant will advise you on. Sometimes your Client’s will also have their own requirements because of internal control or compliance. The rule of thumb is to always ask your accountant to help you issue an invoice in compliance with accounting law and then send the draft to the Client together with the contract for approval. Once both documents are approved, your accountant may sign and issue the invoice. Canceling an invoice is a long and fastidious process that should be prevented if possible!
Concerning the subject of the VAT invoice, it has to be in line with the business activities that are registered under your Enterprise Registration Certificate. A company registered to provide investment advisory cannot provide marketing advisory, at least on the invoice. Issuing invoices for unauthorized or unregistered activities is an offense punished by law. Regarding foreign capital companies, you may as well fail the annual mandatory audit if your VAT invoices are not redacted properly.
So please contact your accountant or legal advisor if need be!