If revenue is already categorized, how do I attach it to an invoice? The tiles that were suggested don't show on my QBO. I am quite lost! Thank you

I'm here to help you match your transactions with ease, @DrStewart. 

Once your entries are categorized, it means that they're ready for reconciliation. Thus, it can't be matched.

Here are the steps on how to undo the categorized transactions and match them:

1. At the left navigation panel, select Transactions.

2. Go to Categorized and click Undo on the transaction you want to undo.

3. Go back to For review.

4. Choose the transaction you want to match and click Confirm.

For future reference, here's an article that could help you understand reconciliation better: Reconcile an account in QuickBooks Online.

Let me know if you have any questions about matching transactions and invoices. I'm always around to assist you. Have a wonderful day!