Actually, fed up referring folk to post #177 so here it is copied and pasted. However, I note from other posts that Firefox browser (available from Amazon store) might be a viable alternative to Silk as well.
SIDELOADING THE APP
Didn't work. I have a Fire TV Stick 2020. So I tried downloading the RangersTV App version 1.1 from APKPure using Downloader. The file downloaded fine. The file installed absolutely fine. However, when trying to Launch it, absolutely nothing happens. So, I guess the theory that it will work on Fire TV OS7 doesn't hold up. Albeit my error was not the parsing one referred to earlier. Now uninstalled.
USING SILK
Now, on my Fire TV Stick playing Live works well. I can go to the RangersTV website, login, click on the Watch Live next to the St Johnstone game and it plays tickety-boo and can be adjusted to full screen by using the Full Screen icon at the bottom. Main issue here is when trying to Login on Silk if I enter my email then click on Next then enter my Password and click on Next it doesn't like it. I found I had to enter my email, then hit the Back button on the remote and then do the same with the Password entry. Often, at that point I got thrown out. Perseverance saw me eventually get Logged In.
The problems come with playing videos on the website. There's a white bar across the bottom of the screen with Up Next on it that prevents you seeing the play button. You can use the remote and press centre+up concurrently and the screen moves up to reveal the Play button, and it will play, but when you then try to click on the Full Screen icon you get thrown out. There's also an issue of getting thrown out if you try to hit the Unmute button.
USING TV BRO
The answer to BOTH the logging in problem and the issue of playing videos in full screen is as mentioned earlier in the thread - TV Bro. Download and install a new browser called TV Bro. Works like a dream. You can use the Submit button after entering your email and it moves to Password. You can enter your password and click Submit and it takes you back to where you can press Login. Fantastic. Even better, once into RangersTV you can select a video and, whilst the white bar of death with Up Next on it will still be there, you can use the centre+up buttons to move the screen up, hit the Play button then immediately pause and scroll to the Full Screen icon and it will work for you. Hey Presto, videos playing in full screen with audio (no need to find and use Unmute button).
So, how do you get it and install it. The full process is detailed at the bottom of the link below. Make sure you scroll all the way down to the section about Fire TV Sticks.:
The following guide will provide you with instructions to install the Best Browser for Android TV devices. This browser is called TV Bro and is working
troypoint.com
Once you've installed TV Bro you will be asked to confirm you want to use Google as your default search engine (or pick another one from the drop-down menu). That will then leave you at a sort of Home page with a list of various websites. Hit the Back button on the remote and you get to the navigation screen. Simply move the cursor to the entry bar where it says about:blank and type in the RangersTV website details:
https://www.Rangers.co.uk/tv#/
The RangersTV page will load. At this point I pressed Back on the remote again to get the menu back. I clicked on the Star symbol top-left and set the page as a Bookmark. Thereafter its just a case of Logging In and away you go. Its a much smoother experience than using Silk. Just use it as normal for Live matches. For videos where the white bar of death appears use the remote for the centre+up combo to get the screen to move up and reveal the Play button. Once you've done that hit the centre button on the remote to Pause and then move down to the Full Screen icon and select it. Video will play full screen, with sound, with no issue.
When you are finished playing a video simply Pause it. Scroll to the Full Screen icon and minimise to get to half-screen again. If you can see the big X in the top right corner to close the video then click on it. If you cannot then use the remote, but this time with the centre+down combo, to scroll the screen down to reveal the big X to close the video.
Personally I found the experience of using TV Bro to view RangersTV much, much better than using Silk which, to be fair, works fine for everything else. Give it a go.