An invoice and a proforma invoice are the same thing, except that the proforma is there so You dont need to put it in the bokkeeping yet.
Just print normal invoice with proforma text on it.
It will be convenient, clever and legal to have a different numbering series for proforma invoices.
You can cancel proforma invoices easily, as they dont "count" as invoices, in bookkeeping terms.
This is a big deal everywhere else, where there axists a value added tax.
The US is afaik the only major economy that does not yet use value added tax.
The proforma is an invoice for all parties to agree on cost and conditions of shipment, and for declaring values at customs.
It does not (necessarily) generate accounting entries in bookkeeping.
Thus you would have an "in-process" entry, and not a receivable.
Where value added tax is used, generally you need to pay the tax independently of whether you have received the payment.
Generally cross border transaction have zero value added tax between companies (in the EU, unless one part is not registered as an Intra Community Operator for VAT).
For you guys, its simple.
For us in the EU, as well.
Some accountants will want to make it complex, but as far as I see only to generate work and fees for themselves.
There is no legal requirement for anything special.
For clarity and safety, always keep a paperwork trail of all invoices, proforma and not.
And then generate an invoice for the goods, referring the proforma nr.
This is to avoid the appearance of VAT fraud etc. which is a big deal in the EU.
I have lots of experience in the matter over the last 20+ years, and have always found dealing with the tax people in the government painless and easy.
I have always had paperwork, as well - and the two are very closely related.
The form, details and type of paperwork dont really matter, ime, at least in finland, UK, spain, hong kong and the us.
Invoices need to state goods, date, serial nr and sender and receiver.
A tax id is mandatory in some countries - although commonly not used in the us (or hong kong or china).
You can add anything else you want, but dont need to.
If a particular invoice is missing a detail, in case of audit, it is no matter.
Tax authorities know all about different customs in different countries.
What is a biggie is tax fraud - but that would be typical of only one invoice, etc. and that missing details and zero supporting documents.
Where physical goods, machines, tools metal pieces etc are involved its an easy, clear matter.
Goods were made and shipped and received and payment was made. Or not.
As long as the payments, documents and shipments match, you are fine.
If you are missing 100.000 kg of steel, machine, screws or something, or a million dolllars worth of "stuff" you will be likely asked where it is.
If you have a shipping document, packing list, and or customs declaration, you will be fine.
The system is geared for and meant to catch people whose bookkeeping shows a loss, or 10$ profit, and there is a misterious single entry for "shin han wan machine tool company", or say "Honest Abes Machine works" with no offers, orders, payments, letters, credits, guarantees and a 1M$ loss on "goods not received", "lost", "not ok" etc.
And you cannot document what goods, where and what happened to them.
Or any claims. Or where the !M$ came from. Etc.
Its common sense, no more.
I have been audited and asked for audits myself on my companies and done special trades multiple times.
In all cases it was painless, and went as I expected.
In case of doubt I have often gone to the tax office, gotten a meeting, and gone to ask specifically about cases.
They have always been helpful, and almost always useful and knowledgeable.
The tax office(s) help you for free, and their decisions carry weight, unlike accountants and lawyers.
If needed, after a meeting, to conver yourself, you can write them a memo and or an email, refer to what you asked and what you understood.
Ask them to deny or confirm it, if you want.
It will greatly help you if it ever comes up later.
This was important, for example, in shipping 5M$ worth of machine tools without VAT in a cross border sale.
If I did not have documents, and there was an audit, I was resposible for the 22% VAT on the import independently of whether I had sold the goods or not.
Plus penalties.
If I had a tax office approved opinion, I was golden.
In Spain, and mostly in general, a decision in your favour is binding. They cannot change their minds against you later on.
Its also free to ask.
Best Hannu