Are you able to confirm if you had bought your domain on the Shopify platform or is it hosted by a Third Party?
Has it been quite a while since you last re-opened the store? In the case that you may need to renew your domain (depending on how long the store has been closed and renewal date for domain).
Nia | Social Care @ Shopify - Was my reply helpful? Click Like to let me know! - Was your question answered? Mark it as an Accepted Solution - To learn more visit the Shopify Help Center or the Shopify Blog