Well, currently I am using plesk 12.5 and there is not much more info I can tell you, in whmcs the module is pretty simple with its config:
http://prntscr.com/cq51e3
After that I do not know what is making plesk telling me that the subscription is not synced. I know that there is an input log in plesk with the data that is being sent to it, but do not remember where, maybe there appears what is going wrong, but no idea.
Thanks