All the whmcs pages are showing, so it sounds like the integration went well, except for a couple of things.
First, my whmcs is in a folder called sales. WordPress in a different folder. I thought I'd mention that just in case it makes a difference.
Now instead of the url being sales/cart.php is now hosting/portal/cart.php/?
Is it ok to remove the /? in the url?
Next, I lost colours.
When I'm logged in as a client and I'm on the page "My Domains" the page is completely white. The text is there everything works fine, but no colour background to define what's active and what's not and so on.
Even at the bottom where it says "Active, Pending, Pending Transfer, Expired/Cancelled, Fraud" is all white. You know like Active used to be green, then there was pink and grey and so on for the others.
And this goes for the menu as well. "My Details, My Service" and so on. The menu is there but background is all white. It use to be black. But this I don't mind. It looks ok with the white background.
Next, I'm on the cart.php page "Shopping Cart" shows twice one above the other. One is green the other blue. Also one is bigger than the other. The same goes for Portal Home page.
That's about it as far as I can tell right now.