We had been working on adding an IDN addon domain in cPanel and received invalid domain name.

Internationalized domain name – Wikipedia
An internationalized domain name (IDN) is an Internet domain name that contains at least one label that is displayed in software applications, in whole or in part, in a language-specific script or alphabet

Domain cannot be added directly in cPanel because domain contains at least one label

Domain Name : lamé.com

We need to use below converter to convert the IDN to ASCII

http://idna-converter.com/?decoded=lam%C3%A9.com&encoded=&doencode=Encode+%3E%3E

Unicode url/domain: lamé.com

ASCII/Punycode (ACE) : xn--lam-dma.com

Once domain is converted in ASC can be added in cPanel.