Don't sweat, @userfinance6. I'm here to help customise your sales receipt and payment voucher in QuickBooks Online (QBO).
You can go to the Custom form styles and customise your Sales receipt template from there. Here's how:
In your QBO account, click the Gear icon and select Custom form styles.
On the page, select Sales receipt from the New style drop-down.
Then, customise your template the way you want to.
Click Done once finished.
But for the payment voucher, if you're referring to the invoice payments (Receive Payment) or Bill payment template, this option is currently unavailable in QBO. QuickBooks can only customise sales forms like invoices, sales receipts, and estimate templates.