First you need to know model of your TV. You can find it on back of your TV:

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SS IPTV for Samsung is no longer in the official app store, but you should not worry because just following the instructions of any of these videos, you can install SSIPTV on Samsung Smart TV 2019.
Sony Smart TV SS IPTV may be installed from official LG Smart World on this platform, in any country.
The first application is called Smart IPTV or Siptv and is available on the Samsung App Store and can be downloaded easily. This application will help you turn on IPTV on your Smart TV. The app itself does.

Regardless to your country, SS IPTV can be found on the LG official store. Just go to LG Smart World and you will find it under the name of SS IPTV. SS IPTV app Samsung Smart TV. Again, Samsung permits its Smart TV users from all around the world to download the SS IPTV app from Samsung Smart.

Or you can find it in settings of your TV, section Support → Contact Samsung:
It's two ways to install SS IPTV in dependence of your model.
If you have D, E, F, H-series or J-series, the procedure is as follows:
1. Download this file - click here
2. Extract the zip file. You can use WinRAR or 7zip.
3. Rename extracted folder to 'ssiptv'.

Samsung Smart Tv Iptv

4. Copy this folder to USB.
5. Insert USB to TV.
6. Enjoy the SS IPTV.
Another (better) way:
1. Open Samsung Apps and go to login page. (Or Settings -> Smart Hub -> Samsung Account, depending on your model.)
2. Login as username: develop and no password.
3. Click on My Apps -> Settings -> IP Settings. (Or click and hold on some app from Smart Hub [Not in the store!] and then click on IP Setting - again, depending on your model.)
4. Set IP to 91.122.100.196.
5. Go back. Now click on Settings -> Start App Sync (Or click and hold on some app from Smart Hub [Not in the store!] and then click on Start App Sync. I don't wanna repeat it, you know.)
Video tutorial: https://www.youtube.com/watch?v=n5cXsCziaXI (random found on the Internet)
FAQ for D, E, F, H-series and J-series:
If the SS IPTV is installed, can I remove the USB? (Question for first type of installation only)
No, you can't. If you remove the USB, SS IPTV will disappear. Of course, if you insert it back, it will appear again. But you can still use it as storage for photos, videos, ....
I have another question which is not shown in FAQ.
Write it under this thread, I will try to answer it.
If you have J or K, the procedure is so difficult.
1. Download Tizen Studio and file tizen.wgt
2. Install Tizen Studio.
3. After install open the Package Manager, don't restart.
4. Install 'Baseline SDK' from 'Tizen SDK Tools' in Package Manager.
5. After that restart your computer.
6. Open Tizen Studio.
7. Connect to your TV:

What Is Smart Iptv Samsung

a) Open Remote Device Manager.
b) Turn on your TV and go to My apps. (from Smart Hub).
c) If you are in My apps, on remote control press 1, 2, 3, 4, 5.
d) Turn on developer mode and write local IP of PC where Tizen Studio is installed.
e) Turn off your TV, then turn on.
f) Press Scan in Remote Device Manager.
g) You'll find your TV. Toggle the switch to on.
8. Create a certificate.
a) Open 'Certificate Manager' through Alt+Shift+C.
b) Click on '+'.
c) Select Samsung, next TV, Create a new certificate profile (name it as you like), Create a new author certificate, enter Author name and Password (as you like).
d) Now you have to login to Samsung account. Register or login.
e) Select backup path (as you like).

f) Select Create a new distributor certificate.
g) Check if your TV is added (DUID).
9. Import tizen.wgt.
a) Select File → Import → Tizen Project and tick Archive file.
b) Specify the location of file tizen.wgt.
c) Change version of project to tv and 3.0 and tick the project.
10. Right-click on the project imported and select 'Build signed package'
11. Now right-click again and select Run as → 1 Tizen Web Application
12. App will start. Enjoy.
UPDATE: As @Florin9doi noticed, it is required to downgrade Tizen Studio. Here is his post.
FAQ for J and K series:
My TV is not shown in Remote Device Manager.
That's because your TV has turned on function 'Instant On.' You have to turn off it in Settings → System → General → Instant On. After that check in My apps if the PCs IP is set.
Can I turn on function Instant On after installing?
Yes, you can.
Have I to start PC whenever I want to start SS IPTV?
No, you haven't. You can remove Tizen Studio, too.
Update: Not true! Every time you turn off the TV it wipes out the TV and you have to install it again. (That's updates from my Samsung TV, if it's not right, please tell me to DM. Thanks!)
Update#2: I tried SS IPTV on Samsung MU6172 and it didn't remove. Half a year without any problem, so it could be a problem just for J/K series.
I got an error 'Installing the package... > Fail'
That's because your TV doesn't have accepted your certificate. Right-click on connected TV and select Permit to install applications.
I have another question which is not shown in FAQ.
Write it under this thread, I will try to answer it.

Smart IPTV on Samsung Smart TV

Samsung has suspended the app from the Samsung Apps Store without notice.

DO NOT uninstall it, if you want to keep the already installed application working on your TV.

Attention! If you have an application installed using USB method stuck at 'Loading', when opening VODs (movies) on your TV, just re-download and reinstall the USB app from the application website again or uncheck the 'Save online' checkbox when uploading your playlist.

You can manually install the app by using the following options:

Tizen TVs (J/K/M/N/Q/R/T):

Extract (unzip) the contents of the following Tizen Widget file to the root of the USB drive (FAT32 format) and insert it to your TV’s USB slot. Make sure the userwidget directory is located in the root of your USB drive. The application will appear on My Apps screen among other apps. You can then remove USB flash drive from your TV (except J series).

On J series Tizen TVs, you can try turning off Menu -> Smart Hub -> App Auto Update to avoid losing the application on every TV restart. Otherwise, there is no solution available.

non-Tizen TVs (E/ES/F/H/J4/J52):

Extract (unzip) the contents of the following Orsay Widget file to the root of USB drive (FAT32 format) and insert it to your TV’s USB slot. The SmartIPTV directory should be located in the root of your USB drive. The application will appear on a Samsung Apps screen among other apps. You can then remove USB flash drive from your TV (not on all TV models).

You can also use Sync server IP address to use in developer mode.

Important! The application does NOT work on D series or older Samsung TVs.

Smart Hub -> App Auto Update to avoid losing the application on every TV restart.
non-Tizen TVs (E/ES/F/H/HU/J4/J52):

Extract (unzip) the contents of the following Orsay Widget file to the root of USB drive and insert it to your TV’s USB slot. The SmartIPTV directory should be located in the root of your USB drive. The application will appear on a Samsung Apps screen among other apps.

You can also use Sync server IP address to use in developer mode.

Important! The application does NOT work on D series or older Samsung TVs.

You have 7 days to try out the application. Afterwards, each TV can be activated after one time payment.
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Loading your own playlist

You can upload your own IPTV playlist by following these instructions.

Remote Control commands

P+/P- and Arrows - switch pages, groups, channels and videos
UP, UPx2 - show current programme information
DOWN - show channel history
SELECT (OK), CH LIST - load channel list in play mode
INFO, INFOx2 - show current programme information
Number Keys - channel number selection; '0', PR CH - channel history
RETURN - hide channel list and infobar; Go back to primary list
EXIT - exit the application
P.SIZE, TOOLS, EXTRA - change stream/video aspect ratio
PLAY/PAUSE/STOP - play/pause/stop stream/video (exit video player)
PLAY (long press) - permanent infobar enable/disable
PLAY_PAUSE - play/pause stream/video; show Groups in channel menu
TTX/MIX - enable/disable 3D mode (Side-by-Side)
AD/SUBT - change subtitle track in stream/video (if available)
REC - toggle DVB input on/off
RED - settings in primary list; select audio/HLS track in stream/video
GREEN, GUIDE - EPG information; choose video play mode
YELLOW - show all channels; digital clock or aspect ratio in play mode (option in settings)
BLUE - show Groups; settings in play mode

Changing audio language

Press RED button, select the language, press OK to set the language, press OK (RED, Back) again to hide the window.

Changing subtitle language (in videos)

Press RED button, then press GREEN button or simply press AD/SUBT button, select the language, press OK to set the language, press (AD/SUBT, Back) again to hide the window.

Buffer size

It's possibile to set buffer size in app's settings for your streams in case you have frequent buffering problems. It is not guaranteed that it will help your slow connection or providers' stream issue.

Set the buffer size back to Auto to use default Samsung buffer size.

Lock TV's MAC address

You can lock your MAC address in application settings by using the Lock MAC button to avoid your playlist being reset by somebody else or if you shared your MAC address with some third party.

If you want to remove the PIN, just use 0000 when locking MAC address again.

Setting User-agent property (Tizen TVs only)

You can try using User-agent property in your playlist if your provider requires it. See examples below.

M3U	TXT
Usage
#EXTM3U #EXTINF:0 user-agent='Star Wars',My Channel http://channel.URL #EXTINF:0,My Channel http://channel.URL\|User-agent=Star Wars	epgCode,Channel Name,http://channel.URL\|User-agent=Star Wars epgCode,Channel Name,http://channel.URL\|user-agent:Star Wars
Examples
#EXTM3U #EXTINF:0 user-agent='Star Wars',Brodilo TV http://brodilo.tv/channel.php #EXTINF:0,Brodilo TV http://brodilo.tv/channel.php\|User-agent=Star Wars	brodilo,Brodilo TV,http://brodilo.tv/channel.php\|User-agent=Star Wars brodilo,Brodilo TV,http://brodilo.tv/channel.php\|user-agent:Star Wars