Thank you
We appear to get a similar however not the same issue when we attempt to update your Joomla installation...
403 Access forbidden.
I notice the following errors which may be related (eg. forbidden access as the temp folder is not available)
The PHP temporary folder is not set.
This folder is the folder that PHP uses to store an uploaded file before Joomla can access this file. Whilst the folder not being set isn't always a problem, if you are having issues with manifest files not being detected or uploaded files not being detected, setting this in your php.ini file might fix the issue.
Warning PHP Upload Size bigger than POST size.
The value of the upload_max_filesize in the php.ini file is greater than the post_max_size variable. The post_max_size variable will take precedence and block requests larger than it. This is generally a server misconfiguration when trying to increase upload sizes. Please increase the value of post_max_size to be greater than the value of upload_max_filesize.
I hope this helps.
Ciaran