MMY APK not installing: match the message
When the MMY APK will not install, the message on screen points at the cause. Match the message before changing settings.
There was a problem parsing the package
The file did not arrive whole. Compare the size with 20,954,528 bytes. If it is shorter, delete it and download again, ideally on Wi-Fi. A browser that renames the file to .apk.bin or .zip produces the same message; rename it back to .apk.
The other cause of a parse error is the Android version. minSdkVersion 24 means Android 7.0. On anything older the installer reports a parse error rather than saying the version is too low. Check Settings, About phone, Android version.
App not installed
On a phone that has never had MMY, this almost always means the CPU does not match. The package carries arm64-v8a native code only. A 32-bit handset cannot run it, and there is no setting that changes that. Phones from about 2019 onward are arm64; older entry-level models are the ones to suspect.
On a phone that already has MMY, the same message means a signature or version-code clash. That case is on the update page, because the fix is different and uninstalling is not always the right first move.
Not enough space
The download is 19.98 MB, but installation unpacks it and the first launch fetches assets. If the data partition has under 150 MB free, the install dies partway and leaves a confusing error. Clear cache from Settings, Storage, or move photos off the device, then retry.
Install blocked, with no other detail
That is the unknown-sources gate. Android 8 and newer ask per app: Settings, Apps, the browser or file manager you used, then Install unknown apps. Enable it there. A work profile or a family-link account can block sideloading entirely, and no toggle inside the profile overrides the administrator's setting.
What will not help
- Turning the global unknown-sources switch on. It was removed in Android 8.
- Renaming the package or editing the APK. Any change breaks the signature and the installer rejects it.
- Downloading a second copy from another site because it claims to be smaller. The measured file is 19.98 MB; a page advertising a 39 MB or 42 MB MMY file is describing a different file.