System is not letting me add new customer in Estimates
Let me show you how to add a new customer, millfixr1.
Aside from the Estimate page, we can also add a new customer on the Customers page. Select Customers from the Sales tab, then click on New customer. Enter all the details and select Save. Create a new estimate and select the customer on the Customer drop-down.
Let's also perform some troubleshooting steps so we can avoid the same problem again. It's best to make use of the incognito window in doing your tasks. It won't save junk files called cache which can result to errors in QuickBooks Online. We can also clear them to see if this is what causing this behavior. Aside from that, make sure that your browser is up-to-date. You can also use a different one if there's available.
I've included these articles related to customers and estimates: