Let an app install on your Android TV
Android TV asks for permission before it installs an app from outside the Play Store.
You give the permission to one app only, the one doing the installing. Nothing else on the TV changes.
Try the first way. If it works, you are done and can skip the others. Go to the next way only when the one before it failed.
On most TVs the first way is enough.
1 Use the message on screen
When an install is blocked, the TV shows a message with a Settings button. Choose it.
The TV opens a list of apps. Find the app you install from, for example Simple Downloader, and switch it on.
Press back. The install continues.
If the first way did not work
2 Open the setting yourself
No message on screen? The same list is inside Settings. TV makers put it in different places, so try these:
Settings → Apps → Security & Restrictions → Unknown sources Settings → Device Preferences → Security & Restrictions → Unknown sources Settings → Apps → Special app access → Install unknown appsDoes Settings have a search box? Type unknown and you will land on it.
If neither way worked
3 Switch on developer options
Use this when the list is missing, when your app is not in it, or when the switch refuses to stay on.
Some devices hide the permission until developer options are on: the Google TV Streamer, the Chromecast with Google TV and a few TV brands. Older Android TV sets rarely need it.
Open Settings and look for About. Google TV keeps it under System, older Android TV under Device Preferences, and some TVs in the main list.
Go to the last line on that screen. It reads Android TV OS build, or only Build. Select it and press OK again and again.
After a few presses the TV counts down the presses that are left. Stop when it says you are a developer: seven presses altogether.
If it says you already are a developer, the option was on before.
Go back to the first or second way. The switch is there now.
Is it safe?
Yes. This is what the permission does
Every app store other than Google's installs apps this way. It is a standard part of Android.
Only the one app you allowed can install anything, and Play Protect keeps checking the TV.
Allow only apps you trust. When the install is done you may switch the permission off again.