extend, installation

Hi everybody,
first time here. So anyone has a tip in the following thing:
I tried to install new modules under “Extend”, but drupal doesnt do it.
no error message, just goes back to “home”
The module I wanted:
https://ftp.drupal.org/files/projects/devel-8.x-1.0-alpha1.tar.gz
my version is Drupal 8.1.9.
Thanks in advance for any help
Birgit

Drupal version: 


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