You are reading this article because we sent you a proforma invoice to be paid, you paid it and then we sent you a tax invoice and it has a different number on it.
Much like any normal business, we work on the proforma invoice system whereby we will issue a proforma invoice for the amount to be paid and when we receive the payment, we issue an official tax invoice and assign it the next number in the numerical sequence of tax invoices.
For example, we send you proforma invoice number 100. You then pay that invoice. Our system will then mark the invoice as paid and retrieve the next available number in our [tax] invoice system and then send you an official tax invoice with that new number.
So if the next number in the tax invoice sequence is 49, then we will send you back the tax invoice with invoice 49.
As a courtesy, we will also mark on the tax invoice, the number of the proforma invoice so your bookkeeper can easily track the two references.
Why do we do it like that?
The Spanish tax office requires us to maintain our tax invoices in an orderly numerical sequence. This is so that in a tax inspection it's for them (and us) easy to reconcile/track the invoices.
The issue that arises with issuing tax invoices though, is that as soon as we create a tax invoice, the amount of tax shown on the invoice is due to the tax office in the next quarter. After all, as a company registered with the Spanish Tax office, we are legally responsible for gathering taxes on behalf of the tax office and sending it to them through quarterly tax returns.
So, if we continually created tax invoices and they are not paid on time or not at all, we as a company are still liable for paying that tax to the tax office in our next tax return because we have declared the amounts in our tax invoices showing that taxes have been gathered/charged.
This is regardless of whether the invoice is paid or not. The tax office is not interested.
If we have declared tax invoices to them with an amount appearing on the invoice, they do not care if it's paid or not, they want the taxes due.
Sure, we could try an omit/exclude unpaid tax invoices when doing tax returns, but that would arouse suspicion and attract a tax inspection because there would be gaps in the numerical sequence of invoice numbers, which as we said is a requirement of the tax office in the first place.
Hence, this is why we will issue a proforma invoice first, because we can literally generate as many as we want, and only generate a tax invoice when we have, well, physically gathered the taxes on behalf of the tax office.
The upside is, if you are a business on the receiving end of our tax invoice, then you can present our tax invoice to the Spanish tax office through your accountant, and legally reclaim the paid taxes (if you are entitled to do so).