I’m having a problem creating an invoice for one of my customers.

Allow me to assist you through creating an invoice in QuickBooks Online (QBO), @esaneson. 

However, to provide you with the best possible solution, it would be really helpful if you could share some more details about the specific issue you're facing. Meanwhile, we can go ahead and check if it's a browser-related issue. 

We can start by opening your account in a private window as it ignores historical data. These are the keyboard shortcuts:

• Mozilla Firefox: CTRL + Shift + P
• Microsoft Edge: CTRL + Shift + N
• Google Chrome: CTRL + Shift + N
• Safari: Command + Shift + N

If you can create an invoice after this, then the issue is likely caused by your browser. You'll want to clear your regular browser cache. If the issue persists, you may need to use another supported browser.

Additionally, feel free to visit this article to guide you through the process of creating an invoice.

To have QuickBooks automatically process your customer payments in the future and categorize them into the correct accounts, you can visit this article for reference: Record invoice payments in QuickBooks Online.

I'll be on the lookout in the comment section for your response on more invoice and QuickBooks-related queries. Take care.