Sending an invoice is not a formality. The email you wrap around it decides whether the invoice gets paid this week or sits unread for three. Get the attachment, subject line, body, and timing right, and the invoice pays itself.
Attach the PDF or send a link?
Attach the PDF. Accounting teams run on PDFs. They download attachments into folders, forward them to approvers, and file them against purchase orders. A link to an online invoice breaks that flow: links expire, get caught by spam filters, and often require a login the approver does not have.
Send a payment link instead only when the client pays through the link itself, such as a card checkout page, or when you bill a consumer who pays from a phone. For business clients, attach the PDF and put the payment link in the email body. The PDF gets filed and the link gets clicked. BCC yourself on the send so you can produce proof of delivery in one search if a dispute ever comes up.
The subject line formula
The subject line does two jobs. It lets the client's finance team route the message, and it lets the client find the email again weeks later. Follow one formula:
- Invoice [number] from [your business]: [amount] due [date]
Three to copy:
- Invoice #1042 from Nova Design: $1,250 due Sep 5, 2026
- Invoice #1042 attached: $1,250 due Sep 5, 2026
- Reminder: Invoice #1042 for $1,250 is now due
Reuse the same number in every subject line for the same invoice. Follow-ups that repeat the number stay in one searchable thread. Clients search by invoice number; if it is missing from the subject, the email survives only if the client remembers your name and the month, which they will not.
Four things the email body must say
The body routes the invoice to the right action. Cover four things, in this order:
- What is attached. Invoice number, total, and due date in the first sentence.
- How to pay. Bank details, payment link, or PayPal address. Never write "payment details on request", which creates a reply loop.
- What happens next. One line: the files are delivered, or phase 2 starts once this is settled.
- Where to send questions. Your reply-to address, plus a request to flag anything that looks wrong.
Complete body in five sentences: "Hi [Name], invoice #1042 for $1,250 is attached and due September 5. Pay by bank transfer using the details on the invoice or by card at [payment link]. The final files are in my email from Tuesday. If anything looks wrong, reply and I will fix it today. Thanks, [Your name]"
Keep the body under five sentences. The invoice carries the detail; the email only needs to route it.
When to send it
Send on the day you deliver the work, while the client's attention and goodwill are at their peak. Waiting for month end adds two to four weeks to your payment cycle for no gain: approval happens in hours, not weeks.
Two exceptions. Retainer or subscription clients that run one monthly payment batch get the invoice at the start of their payment run, with Net 30 terms if that is what their accounts payable expects. And avoid Friday afternoons and Mondays. Emails sent Tuesday to Thursday mornings get opened and actioned fastest.
When you sent it wrong
Wrong recipient: send a corrected email to the right person with one line: "Apologies, this was sent to the wrong contact. Sending it to you directly." Do not resend silently and hope. The correct recipient gets the thread, and the wrong one has no action to take.
Wrong amount: do not edit a sent invoice. Issue a revised version with the same invoice number plus a revision marker, INV-1042-R1, and mark the original voided in your records. Reference the original in the email: "This replaces invoice #1042, which showed the wrong total." Both sides keep a clean trail, and there is no double payment.
Name the PDF so it survives
Accounting staff download attachments into shared folders and rename nothing. A file called invoice.pdf gets overwritten by the next invoice.pdf that lands, and your invoice becomes unfindable. Use this pattern:
- Invoice-[number]-[your business]-[month year].pdf
For example: Invoice-1042-Nova-Design-Sep-2026.pdf. The number is the key field: it matches the subject line and the invoice header, so the client can always pull all three together.
Create the invoice with the fields filled in using the free invoice generator, then wrap it in the email above. A correctly built invoice removes the questions that would otherwise stall the payment.