You have a number of options available.
First ensure an invoice has been raised. See article using invoice as a payment option.
1. Activity Summary tab
In the Invoice Column select on D:1896
2. Activity Request tab
Select on the client name, Jeremy Gandy - Tax Invoice unissued -- $ 100.00
3. Go to Main Menu > Payments > Invoices > Issued
Enter client name in Search then View
4. Then go to $ Pay Options then select Payment Method and Record Payment
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