Currently the sync function decides a domain is either of the following:

1. Active
2. or Transferred Away
3. or Cancelled (if expired, in grace period, or in redemption period).

In other words, the sync will mark the domain as "Cancelled" immediately after its expiration time without account for the fact that a domain enters "Expired" status after this time. This creates some troubles, for instance, the invoice in WHMCS is not cancelled and the user can still pay the fee to renew the domain, but the problem is that if the service (in this case the domain) is with the "Cancelled" status, WHMCS will not trigger the "invoice paid" actions, which in this case is to send the renewal request to the registrar for the domain to be renewed.

Another issue is that with domains which are in "Grace" and "Redemption", these statuses are not reflected in WHMCS (as described earlier that the sync function marks the domain as "Cancelled" only immediately after its expiration time), thus this creates some troubles where there's extra fees for redemption for some TLDs. Now WHMCS already pays attention to these situations, but only if the domain status is correctly set (either to Grace or Redemption).

It would be more useful if the statuses are set more accurately as:

1. Active, if domain is active at NameSilo.
2. Transferred Away, if domain is Outbound Transfer at NameSilo.
3. Expired (Grace Period), if domain is Expired (grace period) at NameSilo.
4. Expired (Redemption Period), if domain is Expired (restore period)at NameSilo.
5. Cancelled, if not any of the above.

Surprisingly the separate namesilo-domain-sync.php cron file sets the domain status in WHMCS according to the correct ones that appear at NameSilo.