Gzip compression not working

Enabling plugin gives the following message:
---------------------------------
gzip is not working properly:
- Your server may not have the "deflate" module enabled (mod_deflate for Apache, ngx_http_gzip_module for NGINX)
- Another plugin may be interfering with the configuration
If re-checking and restarting does not resolve, please check with your host or open a support ticket with us.
---------------------------------------------
I disabled all plugins but no change.
The website is located on a shared server and I do nothave access to the NGINX config files

I have enabled access through the WPMU dashboard for you
Can you please help?
Many thanks
John