Duplicate name Error Customer Data already exists

Hello All,
I’m getting a duplicate entry error for one of my child table.

I have created a custom doctype “Customer Data” and two child table “Vehicle Data” which is a child of the custom doctype and the second child table “Vehicle Data 2” which is a child table of the “Customer” doctype. What I’m trying to do is, I want the “Customer” doctype to be populated when the “Customer Data” is filled and saved. I have written a code for it as well using “frappe.new_doc”. And the data is being successfully populated except while adding values to child table. That is when the error occurs. When I removed the code to populate the the child table it works fine but I need the child table values in the “Customer” doctype.

Check that child table doctype and see if one of the fields has Unique activated