I added customers onto my invoices but when I click on customers I can only see one customer. Why does it do that?

Let's work together and perform some troubleshooting steps so you can see your customers again in QuickBooks Online (QBO), @kodehall445. 

Before anything else, I'd like to ask for more details about your concern to help us be on the same page. Can you clarify what you mean by "added customers to invoices"? If so, we can only invoice one customer at a time.

However, if you only see a one customer from the Customer field drop-down list, I recommend performing these troubleshooting steps below to sort this out.

There are times that too much historical data in the browser can cause discrepancies that affect the display and performance of QBO, leading to situations where you won't be able to find certain information.

You can open an incognito window and login to your QBO account to help us determine if this is a browser-related issue. Feel free to use either of these keyboard shortcuts depending on the browser you're using:

• Google Chrome: Ctrl + Shift + N
• Safari 11 or newer: ⌘ + Shift + N
• Mozilla Firefox: Shift + Ctrl + P
• Microsoft Edge: Ctrl + Shift + N

If it works, return to your original browser and clear its cache to start fresh. You can also use another supported, up-to-date browser that has already been installed to narrow down the results.

Once done, you can get back and manage your invoices and customers seamlessly in QBO.

Moreover, you may also want to learn how to send gentle reminders to your customers about upcoming deadlines: Create and send customer statements in QuickBooks Online.

Please know that I'm just one post away if you still have concerns with managing your customers. I'm here to lend a helping hand. Take care always.