How can I make the invoice fit a #9 double window envelope?

I'd be delighted to assist you today, @gray-liz.

QuickBooks Online supports size 10 windows since the customer's address is only visible in this envelope.

However, we can change the setup of your window envelope. Here's how:

1. Go to the Gear icon, then select Custom Form Styles under Your Company.
2. Select the form that you want to modify then click on Edit. Note that if this is your first time customizing a form, you'll have to select New Style and choose Invoice.
3. Click on the Design tab, and select Edit Print settings.
4. Put a check on the boxes before Fit to window envelope and Include payment stub.
5. Select Done.

In addition, I'll be including this article that'll guide you if you want to print forms for window envelopes: How to print forms for window envelopes in QuickBooks Online.

If you have any questions or concerns regarding invoices, let me know by hitting the reply button. It would be my pleasure to help you out. Wishing you well. 

QuickBooks Online (QBO) frequently automates updates to transition accounts to the modern default experience, which resets custom invoice formatting. These recurring platform enhancements automatically update your form structures, inadvertently overwriting your saved envelope alignment settings every few months.

As a workaround, navigate back to your existing settings and manually save or apply your preferences after the system rollout. You may refer to this article for more details on these ongoing interface upgrades and structural transitions: QuickBooks Online modern experience becomes default.

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