How to send an invoice: a step-by-step guide

Published Friday 2 October 2026

Table of contents

• Before you send an invoice
• How to create an invoice
• How to send an invoice: step by step
• When to send an invoice
• How to write an invoice email
• Emailing a PDF invoice vs sending over the Peppol network
• Best practices for getting paid faster
• What to do if your invoice is ignored
• Automate invoice reminders with Xero
• Send invoices with confidence using Xero
• FAQs on sending invoices

Key takeaways

• Establish payment terms with your customer before starting work, including when you'll send invoices and payment deadlines, as businesses with longer payment terms are significantly more likely to experience cash flow problems.
• Send invoices immediately after completing work or delivering goods, and use PDF format to prevent unauthorised edits while ensuring your invoice arrives instantly with a digital record.
• Include essential details in every invoice: your business information, customer details, clear description of goods or services, itemised costs with taxes, and specific payment instructions with accepted methods.
• Follow up promptly on overdue invoices by sending a polite reminder the day after the due date, as acting quickly prevents late payment from becoming a habit and shows you take payment seriously.

Before you send an invoice

Before you send an invoice, agree on payment terms with your customer, because the European Commission's EU Payment Observatory (2025) found that longer payment terms tend to mean longer waits for payment in 87% of cases, which puts pressure on your cash flow. This means discussing when you'll bill them (weekly, monthly, or when the job's done) and how long they'll have to pay. Setting expectations upfront prevents surprises and makes it easier to collect payment on time.

How to create an invoice

An invoice is a document that requests payment for goods or services you've provided. To create one:

1. Open an invoice template
2. Add the date
3. Assign a unique invoice number

Include these essential details:

• Your business information: name, address, and contact details
• Customer information: their name, address, and any purchase order number
• Description of goods or services: what you provided and when
• Costs and taxes: itemised prices and any applicable taxes
• Payment instructions: how to pay, when payment is due, and accepted payment methods

For a detailed walkthrough, see the guide on how to make an invoice.

How to send an invoice: step by step

Sending an invoice means delivering your payment request to your customer in a format they can easily process. Follow these steps to send invoices efficiently.

1. Choose your delivery method: decide whether to send by email, online invoicing software, or post
2. Prepare your invoice file: save your invoice as a PDF to prevent unauthorised edits
3. Write a brief email: include the invoice number, amount due, and payment deadline in your message
4. Send and confirm receipt: email the invoice and follow up to make sure it arrived
5. Track the invoice status: monitor whether the invoice has been viewed, paid, or is overdue

Using invoicing software like Xero automates most of these steps and keeps all your invoices organised in one place.

When to send an invoice

Send an invoice as soon as you've delivered the goods or completed the work. The faster you invoice, the faster you get paid.

Here are common invoicing schedules:

• On completion: send immediately after finishing the job or delivering the order
• Interim invoicing: bill periodically during large projects for work completed to date
• Recurring invoicing: send at regular intervals for subscriptions or retainer agreements
• Weekly invoicing: spread invoices throughout the month to smooth out cash flow

Think about your cash flow when setting a schedule, because the EU Payment Observatory's 2024 annual report found that 43% of Irish enterprises faced problems due to late payments in 2023. Sending all invoices on the same day creates peaks and dips in your bank balance.

If timing is a challenge, invoicing software can send invoices automatically so you never miss a billing cycle.

How to write an invoice email

An invoice email is the message you send alongside your invoice to request payment. Keep it brief and include the key details your customer needs to process the payment.

Write an effective invoice email:

• Use a clear subject line: include the invoice number and your business name (for example, "Invoice #1234 from [Your Company]")
• State the essentials in the body: mention the invoice number, total amount, and due date
• Keep it short: limit to one or two sentences since the invoice contains the full details
• Add a polite closing: thank them for their business

Example email:

"Please find attached Invoice #1234 for €500, due on 15 July. Let me know if you have any questions. Thanks for your business."

Ask your customer's accounts payable team if they have a preferred subject line format, such as including a purchase order number.

Emailing a PDF invoice vs sending over the Peppol network

The main difference is format. Emailing a PDF sends a fixed document a person reads, while a Peppol invoice sends structured data that software can process automatically.

When you email a PDF, you attach a fixed, human-readable document. The recipient opens it and keys the details into their own system by hand.

A Peppol invoice is a structured, machine-readable data file. It uses UBL 2.1 XML built on the EN 16931 European standard, known as Peppol BIS Billing 3.0. Rather than arriving as an email attachment, it passes between two accredited Peppol Access Points.

Here's what changes for the recipient:

• With a PDF invoice: someone reads the document and re-keys the details into their system, which is slower and more prone to error
• With a Peppol invoice: the data lands directly in the recipient's accounting or enterprise resource planning (ERP) system, ready to process without manual re-keying

Both the sender and recipient need to be connected to the Peppol network through an Access Point for this to work.

In Ireland, this change is already under way. Public bodies accept structured electronic invoices, and mandatory business-to-business (B2B) e-invoicing through Peppol is scheduled to begin for large corporates from November 2028.

Best practices for getting paid faster

Getting paid faster starts with how you send your invoice and how closely you track your outstanding invoices. Email is a reliable method because it arrives instantly and creates a digital record.

Follow these best practices:

• Confirm receipt after your first invoice: call or email to check they received it and understand the details
• Send invoices as PDFs: use formats that can't be edited to prevent fraudsters from changing your payment details
• Offer online payment options: let customers pay by credit card, debit card, or bank transfer directly from the invoice
• Use invoicing software: send online invoices that are secure, trackable, and allow instant payments

Always double-check you're sending to the correct contact before hitting send.

What to do if your invoice is ignored

If your invoice is ignored, follow up promptly with a polite reminder, especially since the Atradius Payment Practices Barometer for Ireland (2025) found that 42% of the value of business-to-business invoices in Ireland was overdue, keeping pressure on your cash flow. Having a follow-up process is essential for getting paid on time.

Before the due date, send a gentle reminder a few days ahead so the invoice stays on your customer's radar. A short note works well, for example: "Hi, just a quick reminder that Invoice #1234 for €500 is due on 15 July. Let me know if you need anything."

After the due date, follow up the very next day with a polite but firm message. For example: "Hi, Invoice #1234 for €500 was due yesterday and appears unpaid. Could you let me know when I can expect payment?"

Make a phone call if written reminders go unanswered. A quick conversation often resolves the issue faster than email and shows you're serious about collecting.

A repeatable process like this helps you reduce payment delays before they build up. Acting fast prevents late payment from becoming a habit.

Automate invoice reminders with Xero

Automated invoice reminders send follow-up emails on your behalf when payments are overdue. This removes the need to manually chase every late invoice.

Here's how invoicing software handles reminders:

• Tracks all invoices: keeps a complete list of sent invoices and their status
• Monitors payments: matches bank deposits to outstanding invoices automatically
• Sends reminders: emails customers when invoices pass their due date
• Escalates as needed: sends additional reminders at intervals you set

You only need to step in when customers ignore automated reminders. Xero's online invoicing system handles this entire process, so you can focus on running your business.

Send invoices with confidence using Xero

Sending invoices promptly puts you in control of your cash flow. The sooner your customer has the bill, the sooner you can expect payment.

To recap:

• Agree on payment terms before you start work
• Send invoices as soon as you finish the job
• Use PDF format and confirm receipt
• Follow up quickly if payment is late
• Automate reminders to save time

With Xero, you get professional templates, automated reminders, and built-in payment tracking to simplify your invoicing, so you can get one month free and see how easy managing invoices can be.

FAQs on sending invoices

Here are answers to common questions about sending invoices.

What's the best format for sending invoices?

PDF is a common format for sending invoices. It preserves your layout, works on any device, and prevents recipients from editing your payment details.

How do I number my invoices?

Use a sequential numbering system that's easy to track. Start with 001 or 1001 and increase by one for each new invoice; include the year or a client code if it helps you stay organised.

Can I send invoices from my phone?

Yes, invoicing apps like Xero let you create and send invoices from your mobile device. This is useful when you need to bill a customer immediately after completing a job.

How long should I wait before following up on an unpaid invoice?

Send a reminder the day after the due date. Acting quickly shows you take payment seriously and prevents late payment from becoming a pattern.

Should I offer multiple payment methods?

Yes, offering multiple payment options makes it easier for customers to pay promptly. Common methods include bank transfer, credit card, debit card, and online payment links.

Do I have to use Peppol e-invoicing in Ireland?

For most small businesses it's currently optional, though public bodies already accept structured e-invoices and mandatory B2B e-invoicing through Peppol is set to start for large corporates from November 2028.