The Client Ledger is a running list of all A/R related transactions related to the current client. From the Client record, select Current Actions, then Client Ledger. This will open a side-panel on the right of the record. Any Payment, Credit or Invoice will show in this view, totaling to the Client’s current A/R balance (which can be corroborated by the A/R report in Client view).
Clicking in the Type column will open the record of the line item selected (i.e. Clicking on the word Invoice in the first line will open that invoice).