Free Domain Voucher請看原文： As a promotional gift, you receive a one year free domain voucher with the initial purchase of a yearly Combo, Unlimited, Pro, VIP, Business Basic, Business Unlimited, Business VIP Premium Plan or Editor X plans. This voucher is only included with the first time purchase of a Premium Plan. It is not included when renewing a plan or upgrading an existing plan. 如果網站使用舊有域名，全部視為續約，恰巧Basic Plan本身沒有送，升級舊有網站也沒有送，所以要付費購買域名。https://support.wix.com/en/article/free-domain-voucher
如果是Basic升級至Combo，或Combo續約，即是使用舊的域名，都不會再有優惠券了