Hi @ackhurstglassltd,
Unexpected behaviors in browsers are usually caused by its stored cache.
To isolate this, I suggest you open your browser's private window. This mode for your browser disables cache, which allows you to determine if it's the culprit for this unexpected behavior.
- Google Chrome: Ctrl + Shift + N
- Microsoft Edge: Ctrl + Shift + P
- Firefox: Ctrl + Shift + P
- Safari: Command + Shift + N
Proceed to add a new customer in the private window of your browser. If that works, go back to your regular browser and clear its cache. Otherwise, open an alternative browser that's available for you.
For additional reference, you can use this article: Add and manage customers in QuickBooks Online. It has the steps on how you can add sub-customers, make a customer inactive and vice versa, as well as merge duplicate customers.
Utilize the comments section below if you have other questions about adding customers to QuickBooks Online (QBO). I'll be around to help you out.
