Can't install xposed framework I want to install the xposed framework on my Nexus 5 and in the framework, the install/update option doesn't work.

My Nexus 5 runs Android 5.0 (Lollipop).
The xposed framework does not currently support Android 5 (Lollipop). More specifically it doesn't work on the ART runtime which is available as a developer option on 4.4 and the only available runtime in Lollipop. You will have to wait for the xposed framework to be updated in order to install it on your Nexus 5 (or downgrade to 4.4 if it's that important).

Ryan's comment appears to show that it's actually the API level but I believe that's a side effect / symptom of running the ART runtime.