I made a custom invoice, but the line items are 1/2 page apart. If I have 5 line items, then the invoice is 3 pages long. Is there any way to correct this?

Yes, there is. You'll have to update your Adobe Reader/Acrobat to the latest version or repair its installation, @RP1015.

Most unusual printing issues in QuickBooks Online (QBO) is caused by an outdated version of Adobe Reader/Acrobat. You can easily correct them by updating or repairing the said program on your computer.

If you're using QBO on browsers for windows, here's how to update your Adobe Reader/Acrobat on the web:

1. Open Reader.
2. Select the Help menu, then choose About Adobe Reader to know your product version.
3. Go to the Adobe Reader Downloads page. 
4. If the web page indicates that a newer version is available, choose Install Now.
5. Click the downloaded file and follow the on-screen instructions to complete the process.

Once done, return to your QBO account and re-print your customized invoice. When the issue continues, I'd recommend repairing your Adobe Reader/Acrobat. For the step-by-step guide, kindly refer to this article's How to repair Adobe Reader/Acrobat section: Update, repair, or re-install Adobe Reader/Acrobat. It also contains details about re-installing Acrobat Professional.

For the complete sets of resolutions when you encounter common printing issues using QBO on a browser for Windows, you can check out this article: Fix printing issues on browsers for Windows.

On the other hand, if you've experienced printing problems when using Safari in Mac OS X, I'd recommend visiting this article for the complete troubleshooting instructions: Troubleshoot printing problems in Safari.

Additionally, you can monitor all your customer payments and the invoices that go along with them by pulling up the Invoices and Received Payments report. This is to effectively monitor your sales and business income. Just go to the Who owes you section from the Reports menu's Standard tab.

Please know that you're welcome to comment below if you have other concerns or follow-up inquiries about printing customized invoices in QBO. I'm just around to help. Take care always.