It deny to enter customer details with similar name while rest of the details are different.

Hello there, info-3hgroup-gma.

In QuickBooks, the system won't allow you to enter the same customer name, though the other information is different. However, I have a workaround that you may consider.

We can add a special character to differentiate the other name. For example, Customer and the other one is Customer1. 

I've also added these articles as your guide in managing your customer's list:

• Manage your customer list
• Add a customer's phone number in the sales transaction
• How to assign account numbers to customers

There you have it, info-3hgroup-gma. I'll be around to help you!