What are e-invoices?

An e-invoice is not a PDF or a scanned image. It's a structured digital document — a machine-readable file (usually XML) that carries the same information a paper invoice would, but in a format the recipient's accounting software can parse and book automatically.

When you send an e-invoice, no one on the other side opens an email and types numbers into a form. The document travels from your accounting system, through an operator network, into the recipient's accounting system, and lands there ready to be approved and paid. The whole exchange happens in the background.

Why e-invoices

• No manual data entry for the recipient — fewer errors, faster processing.
• Mandatory in many jurisdictions for invoicing to public-sector buyers, and increasingly for private-sector ones (B2B mandates are rolling out across the EU through 2030).
• Audit-friendly — the structured format leaves no room for ambiguity.

Standards Sliptree supports

Sliptree generates e-invoices in two formats, picking the right one for the recipient automatically:

• Estonian e-invoice format (version 1.2) — used inside Estonia, routed through the Estonian operator network.
• Peppol BIS Billing 3.0 (UBL) — the European cross-border standard, routed through the Peppol network for recipients elsewhere in Europe (and increasingly worldwide).

Both formats carry equivalent information, so the same source invoice produces a valid document in either standard.

Operator networks

You don't send e-invoices directly to your customer's email. Instead, your accounting system hands the file to an operator — a service that delivers e-invoices the way email is delivered through SMTP. Sliptree is connected to an Estonian operator (for the Estonian network) and to Peppol Access Points (for the European network). The recipient is reached through their own operator, which is registered separately.

What you need to send e-invoices

A quick checklist:

1. Your business must be in a supported country (currently Estonia, Latvia, Lithuania).
2. You must complete the one-time setup — see Setting up e-invoicing.
3. You need an IBAN on file (SEPA bank account). The Estonian format requires it; for Peppol it's strongly recommended so the recipient can reconcile the payment automatically.
4. Your customer record needs a registration number — e-invoices are routed by business identifier, not by email.

When all that's in place, sending is a single click. See Sending e-invoices to customers.