Error: Could not poll for Version while configuring
To be able to solve this error, you need to understand what it means and when it happens, when you try to add or edit a vm configuration, WHMCS initiates a connection to Proxmox JSON api using the local CURL library, this connection was successful and token was returned, but then WHMCS try to send a call to get Proxmox version using this token, here the problem take place, till now i was able to isolate two causes of this.
1- i found CURL 7.31.0 had a bug ( http://curl.haxx.se/mail/lib-2013-07/0157.html), that caused this problem, fixed in 7.32 or use older versions than 7.31, the debug showed curl crashing with
url: (56) SSL read: error:00000000:lib(0):func(0):reason(0), errno 0
2- This error is caused also when node name is wrongly specified in (setup->Product/Services->Servers) on WHMCS side, you need to make sure the node name is the same as shown in proxmox gui, one client set the server Hostname to the long node name kvm2.vmline.pl while node name was showing kvm2 in proxmox gui, what happens node name need to be the same as shown in proxmox gui on left panel, if not then proxmox will go crazy looping through all nodes trying to find the unknown node name and will end up with a an error:
HTTP Response - 500 HTTP Error - HTTP/1.1 500 proxy loop detected
Both above errors, caused the "Could not poll for Version" error. Hope this helps you all.