Can not add the app "Nintex Workflow for Office 365" to office 365 e5 developer license

hello ,

I want to try the Nintex workflow for office 365 but unfortunately I can not add the app because I got

"Sorry, this app is not supported on your server"

I tried to uncheck the option "Block SharePoint 2013 workflows" but no luck the value stuck with check .

if any one experienced this issue ?

thank you