In order to fix HC integration with Whmcs new parameters we have to modify HCAPI, after which HC will start working with whmcs. Which will included all issues fixes which been reported in this thread.
Sorry to say but user will have to wait till build10 to get this new integration.
Build10 first beta is expected on 2nd week of January.

I am using WHMCS since long & It is working good enough. I am having no issue or error with it till now...........