Hello there, @scowan-compel-us.
I'm here to help you keep the process of finding an invoice by amount.
Yes, QuickBooks Online (QBO) can search for a certain transaction in the system. You can use the built-in Search icon in the program to find the invoice using the amount.
Just click the Search icon and enter the amount. See the sample screenshot below.

You can also find the said invoice by pressing CTRL + letter F key on our keyboard altogether. Here's how:
- Click Sales in the left panel and choose Invoices.
- From the Invoices tab, press CTRL + F key on your keyboard.
- Enter the amount on the Finder box.
- This will highlight the transaction with the same amount.

I'm leaving you this article to learn more about searching a transaction in QuickBooks: Search for transactions. It also gives you steps on how to search by customer and vendor names.
Additionally, you can check the following articles for some links about adding and categorizing payments, as well as how to view invoices that are due on a specific date range in QuickBooks:
Please know that you're always welcome to post any questions you have in this space related to the invoices. Have a great day ahead.