I thought my problem had been solved because my Joomla! has updated to v3.6.5.... Not really.
I now want to update to a newer version of a module and neither the manual update nor the installer update work.
check if you have correct permissions on the folders, correct file ownership
In the case of the module directory in question to be installed, the permission is 755.
Both the folderinstaller and packageinstaller are 755 with all the same owner/group number throughout [137363 15000]. And same as on the desired module folder to be installed.
...the code is a command to install php-xml support...
I am assuming that the hosting service provided Joomla! as well. If possible, I would suggest you contact your provider's service and carefully explain the problem.
My host provider only supports WordPress. My installation of Joomla! has been entirely on my own initiative.
But I have another parked Joomla! website on this same account that is installing just fine. So I do not think the issue is with anything to do with the host provider's service.
[In fact, because I have WordPress Essentials installed on my account to gain security features for this domain, the provider's tech support totally bypasses my questions as Joomla! issues and falsely assumes they are WordPress issues.]
These security features scan this domain for malware and say that it is clean...
I just now tried a Discover of uninstalled features, and the module was found and said to have been installed successfully ....[This had not worked previously. In between I reduced the level of security on the parked website.] But it still does not show up in the list of installed modules.
Still not there.