Does your PHP version in Joomlas System > System Information > PHP Information specifically say 7.0.6-1? I'm not finding any official release information regarding the -1 notation on the version. I've upgraded to 7.0.6 and still am unable to confirm your issue.
Is there another PHP 7 release available to you that you could try? Please also check that cURL is available.
If still having issues try making the below change as a last resort to see if issue resolves.
IN: libraries/CBLib/GuzzleHttp/Adapter/StreamAdapter.php
ON: Line 62
FROM:
Code:
$stream = $this->createStream($request, $http_response_header);
TO:
Code:
$http_response_header = array();
$stream = $this->createStream($request, $http_response_header);
krileon
