Sending an invoice sounds straightforward, but how you send it — and what you include — has a significant effect on how quickly you get paid. This guide covers the most effective methods for sending invoices, what to write in the email, how to follow up, and what to do when payment is late.

Step 1: Create a Complete Invoice

Before sending anything, make sure your invoice is complete. Missing fields are the number one reason invoices get kicked back to accounts payable:

Invoice number and date
Due date and payment terms
Your full name/business name, address, and Tax ID
Client's name, address, and PO number (if they require one)
Itemized line items with descriptions, quantities, and prices
Subtotal, tax, and total
Bank details or payment link

Step 2: Choose Your Sending Method

The most common methods for sending invoices are:

Email with PDF attachment — The standard for most freelancers and small businesses. Export your invoice as a PDF (BillZoom lets you download a professional PDF instantly) and attach it to an email addressed to your client's accounting contact.
Email with online invoice link — Some invoice tools generate a shareable link. Less universal than PDF.
Accounting software integration — If you use accounting software, you may be able to send invoices directly from the platform.
Post (physical mail) — Required in some industries or jurisdictions, though now rare. Send a physical copy for high-value contracts or clients who specifically request it.
Invoice platform portal — Some large companies (e.g., government clients) require invoices to be submitted through a specific procurement or AP portal.

Step 3: Write a Professional Invoice Email

Your email matters. A clear, professional email with the right subject line and body ensures your invoice does not get lost or delayed in the client's inbox:

Subject: Invoice INV-001 — [Your Name / Company] — Due [Date] Hi [Client Name], Please find attached invoice INV-001 for [brief description of work], totalling [amount], due on [due date]. Payment details are included on the invoice. Please don't hesitate to get in touch if you have any questions. Thank you, [Your Name]

Key elements: always include the invoice number and due date in the subject line. This makes it searchable for your client's accounts payable team and reduces the chance of it being overlooked.

Step 4: Address It to the Right Person

Ask your client at the start of the project: "Who should I address invoices to, and what email address should I use?" Many payment delays happen simply because an invoice went to the wrong person. For larger companies, invoices typically go to accounts@companyname.com or a specific accounts payable contact, not the person you worked with.

Step 5: Follow Up When Payment Is Late

If your invoice is not paid by the due date, follow up promptly and professionally:

1–3 days overdue: Send a polite reminder. "Just following up on invoice INV-001, which was due on [date]. Please let me know if you need anything further to process payment."
7–14 days overdue: Send a firmer follow-up. Include the original invoice as an attachment again.
30 days overdue: Send a formal demand letter. State that you may apply late payment interest or fees as specified in your payment terms.
60+ days overdue: Consider a debt collection service or small claims court, depending on the amount.

How to Handle "We Never Received the Invoice"

This is a common delay tactic. Best practices to prevent it: always request a read receipt or delivery confirmation when emailing invoices. Request written confirmation ("Please confirm receipt of the attached invoice") in your email. If using a procurement portal, document the submission confirmation number.

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