Unsigned apps are those that aren't available on the Play Store. Every device bans the installation of unsigned programs downloaded from third-party sources by default for security reasons. Even if unsigned apps are prohibited by default, you can install them on your device.
Fixing this issue entails the following steps:
- Navigate to Settings>Lock Screen and Security to install third-party apps on your device.
- Unknown Sources should be enabled.
- You can now install the program.
