Displaying plot with Shiny server

Hello !!

I'm completly stuck with the Shiny-server config ...
I installed shiny-server on Azure VM with centos 7 (I tried also Ubuntu).
But, it's impossible to display / rendering plot in my shiny apps when I run them on shiny-server. I'm attaching screen capture of Hello Shiny page Hello shiny. The slider is present but not the histogram. Can you help me with this issue ?

Thanks in advance.