If you receive the error message "Required parameter missing; Missing required charge agreement extension" when submitting a domain application via the API, this means that you have attempted to register a PREMIUM domain and are missing the class parameter.
The registration of a PREMIUM domain via API must be requested with an ADDDOMAINAPPLICATION command and the corresponding PREMIUM class name.
You can determine the class name with a CHECKDOMAINS command.
For more information, please visit our wiki or our API manual: ADDDOMAINAPPLICATION CHECKDOMAINS