You need to download the appropriate version of Xposed that suites your android version.
You probably tried to install xposed for SDK22. Lollipop is SDK22, Marshmallow is SDK23.
Try Xposed for SDK23, this should work 
You need to download the appropriate version of Xposed that suites your android version.
You probably tried to install xposed for SDK22. Lollipop is SDK22, Marshmallow is SDK23.
Try Xposed for SDK23, this should work