Payment reminder message: the channel changes the wording

The same request reads differently by channel: email is formal and can carry attachments, WhatsApp is quick and informal, SMS is for one line only.

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Email

Subject with the invoice number and the date, body of three lines, invoice attached.

Best for the first and the formal touch: it leaves a record.

One paragraph, no attachments unless asked, and only if you already talk to the client there.

Never send a formal notice by WhatsApp: it looks like an ambush.

One sentence with the invoice number and a payment link. Nothing else fits, and nothing else is needed.

Use it as a nudge, not as a replacement for the email trail.

Invoice number, amount, and one question about a date.

The tone escalates with the number of days late, not with the channel.

Only where you already use it with that client. Otherwise it crosses a line from professional to intrusive.

For a nudge yes; for anything formal you need a written record.