How to Send a Formal Demand Letter for Unpaid B2B Invoices in Spain

A foreign creditor with one or more unpaid Spanish invoices needs a formal demand letter that is not generic. Spanish recovery practice has hardened around a specific letter template that combines four functions in a single document: a structured statement of debt, a quoted statutory interest calculation under Ley 3/2004, an itemised EUR 40 fixed-compensation claim, and a credible escalation timeline. Letters that hit all four functions convert into payment at roughly forty percent on first send. Letters that miss elements either get ignored or, worse, get used by the debtor as evidence that the demand is not serious. This page is a step-by-step on what the letter must contain, how it should be sent, and how it links to the rest of the recovery sequence.

What the demand letter must contain — the five mandatory sections

Section one identifies both parties with full corporate name, NIF or CIF, and registered domicile. Section two is the debt schedule — a numbered table of every invoice claimed, with date, original amount, due date, and days overdue at the date of the letter. Section three is the calculation of statutory interest under Ley 3/2004 at the published BOE rate (currently 12.15% for H1 2026), applied invoice-by-invoice from the day following each due date, plus the flat EUR 40 fixed compensation per overdue invoice. Section four sets the IBAN, transfer reference, payment deadline (typically ten to fifteen calendar days from receipt), and the total claimed including interest. Section five is the escalation notice — a clear statement that absent payment by the deadline, the file will be filed as proceso monitorio at the debtor's competent court, with all judicial costs and external recovery fees added to the principal under Article 8.2 of Ley 3/2004.

The letter is short — typically one to two A4 pages. Long letters lose impact and create surface area for the debtor to dispute peripheral claims. The voice is procedural, not adversarial. The implicit message is that the next step is mechanical and the creditor has no interest in negotiating around the statutory entitlement — only in collecting it.

What changes in the letter for a foreign creditor

Three things change. First, the debtor's identification block must include not just NIF/CIF but the corresponding home-country reference for the creditor, so that the letter and any subsequent court filing connect to the same legal entity. Second, the IBAN provided for payment can be a foreign-country account; Spanish debtors do not have a statutory right to insist on a Spanish IBAN, and SEPA covers the transfer at zero additional cost. Third, the escalation notice should specify that the monitorio will be filed at the debtor's competent Spanish court under LEC Art.813 — this signals to the debtor that the recovery is not abstract but operational on the ground in Spain. Foreign creditors who fail to make this third point clear are routinely filed away as remote and ignorable.

The letter is also where the foreign creditor should make a specific reference to the EUR 40 fixed-compensation entitlement under Article 8.1 of Ley 3/2004. Most Spanish debtors know their lawyer cannot waive this on their behalf, and most Spanish lawyers know the statute since 2022 makes the right indefeasible. A demand letter that itemises EUR 40 per overdue invoice signals to the debtor that the file is being built professionally and that opposition costs will be paid by the debtor under Article 8.2.

Comparison — what good and bad demand letters do for recovery

The economics favour the procedural letter sent via burofax. The cost differential between this and a generic template is one Correos burofax — about EUR 30. The recovery differential is roughly thirty-five percentage points of conversion. For a foreign creditor sitting on EUR 50,000 of overdue Spanish invoices, that is between EUR 17,000 and EUR 20,000 of expected-value recovery moved into the first ten days, before any monitorio cost is incurred. The cheapest discrete spend in the recovery toolkit, properly executed, is the demand letter.

Can I send the demand letter myself or do I need a Spanish lawyer?

Either works. The letter does not require an abogado signature to carry full statutory effect under Ley 3/2004 — the underlying right to interest, the EUR 40 fixed compensation, and the limitation interruption derive from statute, not from the identity of the sender. A Spanish-licensed debt collection agency acting as gestor produces the same legal effect at substantially lower cost than a law firm letterhead. What matters more than who signs is what the letter contains and how it is sent. The letter must be in Spanish, identify the parties precisely, schedule the debt invoice-by-invoice, calculate the statutory interest at the published BOE rate, itemise the EUR 40 per invoice, set a hard payment deadline of ten to fifteen days, and state explicitly that the monitorio will be filed at the debtor's competent court if the deadline passes. It must be sent by Correos burofax with both acuse de recibo and certificación de texto. A letter meeting these requirements, signed by the creditor or by a Spanish-licensed agent, carries the same conversion power and the same evidentiary effect at the eventual monitorio filing.