Thanks for visiting the Community, @matilda-holliday. Let's check to verify if you're experiencing a browser issue by logging in to your company using the incognito or a private window. 

First off, open a default browser, then follow these shortcut keys to open a private or an incognito window: 

• Chrome simply press Ctrl + Shift + N.
• Mozilla Firefox and Internet Explorer, press Ctrl + Shift + P.
• Safari, press Command + Shift + N. Make sure you're using the latest version.

Log in to your QuickBooks Online, then open an invoice and try to type in the customer box. If that works, you'll need to fix your default browser by clearing your browser cache and temporary Internet files.

If none of the steps above worked for you, try another supported browser. 

Feel free to click the Reply button below if you have additional questions. We're always here to help.