Start here: the 30-second checklist
Before anything else, confirm three things: the file is the full 51 MB, you are opening it with an XAPK installer app (not tapping it directly), and your phone runs Android 7.0 or higher. Most failures die at this checklist. If you have not installed it yet, follow the Delta Emulator install guide first.
Parse error
The download did not finish. Delete the file, re-download from the download page, and check the size reads 51 MB. Downloads interrupted by switching from Wi-Fi to mobile data are the usual culprit.
XAPK file will not open
Stock Android cannot open .xapk files. Install a free XAPK installer from the Play Store, grant it storage access, and open the file from inside the installer. If the file is invisible there, move it to the top-level Downloads folder and rescan. The Delta Emulator home page documents the exact 51 MB file size to check against.
Blocked by Play Protect
Play Protect sometimes flags sideloaded apps. Tap More details, then Install anyway. The Delta Emulator file served here passed a malware scan on the bench; the flag is about sideloading, not about this specific file.
App not installed (signature conflict)
An older or differently-signed copy of the emulator is already on the phone. Uninstall every copy, restart the phone, and install fresh. Back up your saves first: the save transfer guide shows where they live.
Still stuck
Note your phone model, Android version, and the exact error text, then mail it to the support address. That is usually enough to reproduce the problem on the test rack.
