Question regarding your plugins

HI is there someone i can get help to install your plugins i have installed on my site cause im getting very confused and frustrated with some of them and they are not functioning correctly i would really appreciate the help cheers !

plugins giving problems are as follows >>>

whmcs
support
classifieds
pro sites

with pro sites the edit checkout page brings up a post from my site . and i dont see a option for users to create a site or upgrade there plan .

with whmcs i dont have a option to sell hostings nor can i find where the link is for the remote hosting it asks for .

with classifieds when i set it to be a paid feature, classifieds does not show up on the user end.

and with support i get a 400 error message when submiting but i was told it was because of the incorrect link i have in the whmcs which i cant find .

so can someone please please help me with all this cause im stressing and its doing my head in cheers !!!