Regardless of the extension, all domain names use the same character rules which must be followed when you search for yours:
You can use letters (a-z), numbers (0-9) and dashes/hyphens (-). Spaces are not allowed, and your domains cannot begin or end with a hyphen. Your web address cannot include special characters like “&” or “!”. However, there are exceptions with IDNs where you are allowed to include special characters from other languages in your domain names.
A domain name cannot be less than three characters long, not including the extension, and names cannot be more than 63 characters so check yours is less than this.