How can I tell whether the problem is with the device rather than the app?

If Android stops the installation before our app even starts, that usually points to a device or security issue and not to a defect in the app itself. Typical signs include messages about “Install unknown apps,” Play Protect, Advanced Protection, administrator policies, or “package conflicts with an existing package.”

Another strong sign is a grayed-out switch under “Allow from this source,” or an active work profile or managed device. Android Enterprise explicitly allows unknown sources to be blocked by policy—in some cases even device-wide.

In practical terms, if the same APK can be installed on another compatible device, or if the Google Play version works but the APK does not, that is a very strong indication of a system-level restriction on the affected device.