Can i adjust an invoice and the amount collected after it has been done?

Hello there, @mosey15.

You can only update the product or service item for a paid invoice. Changing the amount on the original invoice will affect your customer's balance.  You need not worry though, you can void and recreate the invoice then, apply the payments on it. I can share the steps on how to do this.

1. Go to the Sales menu.
2. Choose the Invoices tab.
3. Select the invoice you want to modify.
4. On the Actions column, click the drop-down menu.
5. Click View/Edit.
6. Scroll down to the bottom of the screen.
7. Choose the More link.
8. Select Void.
9. Click Yes, void transaction! to confirm the action.

You can refer to this article for more detailed information: Void or delete an invoice, bill, or other transactions.

Also, for more insights about  managing your transactions, you may check these articles:

• How to undo a voided transaction

• How to use the audit long to re-enter deleted transaction

Keep me posted if you have other questions. I'm just a few clicks away.