What is IDN ?
IDN (Internationalized Domain Name) is a domain name that uses non-ASCII characters, such as ñ, ü, ý, etc. Process to add such domains is simple from cPanel/WHM.
Before adding the domain from WHM, you first need to convert the IDN domain name to Punycode. Once you have the punycode version, you are set to add the domain from WHM. Make sure account username does not use punycode or any non-ACII characters. Simply use plain ASCII characters for usernames.
For example, if the domain name to setup was aüra.com. you need to use as below.
Converting them might be a tedious task if you are new to it. Here is the punycode converter which will help you to convert them at few clicks.