How does an invoice get marked as paid?

For the online rails, it's automatic. When a client pays through Stripe, PayPal, Wise, Razorpay, or SSLCommerz, the payment auto-reconciles against the invoice and the status updates on its own — no manual bookkeeping.

For manual bank transfer, you confirm receipt yourself once the money lands, and Kliently then reconciles it. Either way, the invoice always reflects exactly how much has been paid, and smart reminders stop the moment it's settled so clients aren't nagged after they've already paid.