u/lemonbhosdika

I was facing this issue too, so this is what I did because it definitely worked for me and should work for you as well.

1. If you can’t see your ATV on Sideloadly, you need to forget your WiFi passwords from both your Apple TV and MacBook. Even do it on your iPhone since I have the same ID on everything. Then put your passwords back, lock your phone, keep it near your ATV with your MacBook, and unlock your phone. You should see an ATV pop-up asking to pair. Do that, and make sure you’re in the Remotes and Devices section in your Apple TV settings. Sideloadly will then read your iPhone and your ATV name (not paired), like this.
2. You have to install Stremio or any IPA (just guessing it works for any IPA) on your iPhone first before doing it on your Apple TV. Otherwise, Sideloadly shows an error saying “certificates don’t match.” The fix is to install Stremio on your phone, then go to VPN & Device Management under General in iPhone settings and trust the unknown developer from your fresh Stremio IPA. Once you do that, I think Sideloadly reads the trusted dev code from your iPhone and accepts it for every device you have.
3. Now go to Sideloadly, select “your ATV (not paired),” and install your tvOS IPA. Click start, and a pop-up with a pairing code will show on your ATV. Enter it and continue.
4. While the package is unpacking, I get an error around 60% saying: “FAILED: Call to idevice_new_with_options failed: IDEVICE_E_NO_DEVICE Waiting for the device … to re-appear (will wait for at most 3 minutes).” I tried everything but couldn’t fix this.
5. What I did was install the IPA again and just let it sit on that error for like 2 minutes. I went away for a bit and when I came back, I saw Sideloadly retrying automatically. It started unpacking again, the percentage kept going up, and then I finally saw Stremio on my Apple TV.

Hope this works for you because I wasted like 2 hours figuring this out.