A trex iptv apk download is an Android package on a mirror, not a store listing. Before you tap Install, treat the file as untrusted until the hash and the version string match what the distributor posted. The package format at https://en.wikipedia.org/wiki/Apk_(file_format) is a zip of the app, the manifest, and a signature. A renamed zip with a cute icon is not a signed build.
Sideloading is how the file reaches the box. The overview at https://en.wikipedia.org/wiki/Sideloading is the short version: you copy a package from a PC or a browser, then install it outside the store. On a Fire TV or a cheap Android stick that means unknown sources on for one session, then off again. Leave the toggle on and the next popup can plant a second APK you never asked for.
I run a short check. Download over HTTPS. Compare the SHA-256 against the page that shipped the build, not against a Telegram caption. If the distributor never publishes a hash, skip that mirror. Open the APK in a zip tool and confirm AndroidManifest.xml is inside. Google's Play Protect note at https://support.google.com/android/answer/2812853 is worth a skim even when you skip Play Store: the scanner still flags known-bad packages after install.
Version strings beat "latest" in the filename. A file named trex-iptv-v9.apk that reports 3.2 in the manifest is a rebadge. After install, open About and write the version down. If the player asks for a playlist URL, paste a test list, not your main one, until a couple of channels lock. I keep this Android sideload checklist next to the hash sheet so the next stick does not reuse a stale APK from Downloads.
If the app crashes on launch, the ABI is wrong (armeabi-v7a vs arm64-v8a) or minSdk sits above the stick. That is a bad file, not a bad playlist. Delete the APK. Do not keep retrying the same download.