A quote is an invoice before the work. Send it, see it accepted, turn it into the invoice in one tap.
New › Quote. Pick the client, add the work from your services, set the days. The quote gets a reference (QUO-2026-001) and a valid until date, 14 days by default.
Tap Send by email, or Copy link and paste it in WhatsApp. The client opens a page with the quote and two buttons: Accept and Decline. You get a push either way, and the timeline on the quote shows opened, accepted or declined with the time.
When the work is done, open the accepted quote and tap Convert to invoice. The lines, the client and the dates carry over; you adjust the days if they changed and send.
Every invoice has a due date. When it passes, the invoice turns overdue on the Invoices tab and on Home, and Cowstail sends the client a polite reminder email with the link; you get a push too. Chase by hand from the invoice page with Resend email.
Related: your first invoice, getting invoices paid on time.