From HEXONET Wiki
API RenewDomain
The RenewDomain command is used to renew domains explicitly for a specified time period at the registry . When renewing a domain please enter the domain, the period for renewal (e.g. period = 1) and the current expiration year (e.g. 2007). Please notice that you can not explicitly renew domains under all TLDs. For further information please see the corresponding TLD info page.
IMPORTANT: Please have a look at the Domain API-Manual for a current list of allowed parameters.
COMMAND
(required) command = RenewDomain domain = (DOMAIN) (optional) period = (INT) expiration = (INT)
RESPONSE
(required) code = (CODE) description = (DESCRIPTION) property[registrationexpirationdate][0] = (DATE) property[status][n] = (DOMAINSTATUS)
Please have a look at HEXONET Renewal System to understand how the system internal renewal works.