Add ons in 5.6.3.3 not downloading

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Newly purchased add ons are not downloading and therefore I can't install. They are connected on my project page, but not showing up in my add on list on the site. They are also not showing up in the C-Panel. I have emptied my C5 cache, emptied the browser cache, logged in and out, contact the developer of the add -on and after trouble shooting agree it's a core question.

Any help would be greatly appreciated.

wanderlust