Why can't I install terraria on my android, says "the application is not installed"?

There may be several reasons for this:

1. Your phone's Android version or specifications are not suitable for this game. With this problem, except for replacing the device, nothing can be done;
2. There is not enough free internal phone memory to install the program. To fix this, you need to clear the internal soldering of the phone (it is the internal memory of the phone, freeing up space on the installed SD-card or replacing it with a more capacious situation will not fix it!);
3. If you are installing the game not from Google Play, but from an .apk file, then it is possible that the file is either corrupted, or it lacks a digital signature, or, on the contrary, there is a malicious code that the installer noticed. In this case, it is better to look for another source to install the game.