Let me help share information where you can find the created invoices after sending them to your customers.
When an invoice is saved, it'll be gathered in the Invoices page. You can identify which invoice your customers have paid into by comparing the amount you received.
Additionally, here is an article you can read for the steps about the different methods you can start in manually recording a payment from your customers: Record invoice payments in QuickBooks Online.
Stay safe and comment below or start a new thread if you have any other questions.
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