(UndefinedFunctionError) function Magnify.Web.Router.Helpers.session_path/2 - after installing Coherence

Well the correct way where probably to use the static_path/2 helper:

<img src="<%= static_path(@conn, "/images/logo-dark.png") %>" class="logo logo-dark">

Of course you need to make sure that @conn is available in that partial then, I’m not doing phoenix right now, so I’m not sure if its passed down the road implicitely…