It is not possible to renew an existing domain using the free domain voucher. The voucher is only valid towards the purchase of a new domain from Wix.
Additional Limitations:
The voucher is valid for select extensions only. Learn more about the available extensions when using your free domain voucher.
The voucher does not cover Private Registration or additional years of service which are available for an extra fee.
This article is credited to the Wix team - https://support.wix.com/ and we thank them for that!