Allow WHMCS license to contain both an IPv4 and an IPv6 address
When our license only had our IPv4 address allocated, admins could only connect to the admin control panel using IPv4. If they tried to connect using IPv6 (which happens automatically if possible by the user on our website) then they would be presented with an invalid license error. We reissued the license and when it had the IPv6 address allocated then the same problem happened but with anybody connecting using IPv4. Now that both the IPv6 and IPv4 addresses are allocated to our license this issue has gone away.
To fix this the only way is to contact licensing to manually add both addresses to your license. As IPv6 becomes more widespread this issue will become a major problem down the road so the best thing to do is to add this feature before that happens.