if it's not showing as a installable app check the name the File currently for download is called
com.pulsehavenstudios.dod-Ch4EP2-Publicapk
And will not let you install unless you edit the name and put a period in between Public and apk example:
com.pulsehavenstudios.dod-Ch4EP2-Public.apk
This will make it a working APK file to use
Or just put .apk at the end