which version is for Fiio M11 Pro as there are many from the official Neutron download page via Google in the device.
Fiio M DAPs have no Google Play and do not expose possibility to add e-mail account to the OS, so you can use apk from both sections and add e-mail account to Neutron via Help -> Account -> [+]. For M11 you will need _ARM64 apk. More details here:
http://neutronmp.com/faq/10-fix-no-google-play-services