Invalid common user or role name

You're trying to create a common user, not a container user, with an invalid name:

ORA-65096: invalid common user or role name
Cause: An attempt was made to create a common user or role with a name that wass not valid for common users or roles. In addition to the usual rules for user and role names, common user and role names must start with C## or c## and consist only of ASCII characters.
Action: Specify a valid common user or role name.

If you want to create a user in a particular container then you can use the alter session set container first, so your create is applied within that container. If you really do want a common user, follow the naming rules above.

Read more in the documentation.

I had used below command. It's very useful. So, I would like to recommend to you.

alter session set "_ORACLE_SCRIPT"=true;

For more information, see: http://www.dba-oracle.com/t_ora_65096_create_user_12c_without_c_prefix.htm