Every payment lives in a few connected places, so you can start from the invoice, the client, or the payment itself.
On the invoice
Open any invoice and click the Payments tab. You'll see Total Payments, Total Paid, and Remaining Balance, with a row for each payment — its date, ID, amount, method, and status.
By client, and by payment
On a client's profile — the Payments tab lists every payment that client has made, across all their invoices.
The payment record — click any payment ID (like PAY-1068) to open its own page, with the amount, method, the client and invoice it applies to, and a full transaction history. From there you can Send Receipt or download a PDF.
Related: Collect a payment.