Hi, I'm Nathan.Sorry to hear that you're having trouble with this but I'll do my best to help you.
What app are you trying to download, and from where are you finding/trying?
Where are you finding that app though, are you seeing it within the web browser on the tv?
Which specific model tv do you have?
Okay try going into the samsung settings menu first (not the app menus) and look for the software update function, so we can make sure the tv firmware is on the latest version, then you can try the update again after that.
What is downloading, software update, or app?
Okay if still no change, go into the tv settings menu and choose the factory reset option,
when you're done you will have to reconnect it to wifi, and then you can try the app download again
Can you try another app and see if they respond any better?
Okay that really leaves only the possibility of this being a firmware issue.We can't address that though without the model number of the tv, I need you to find that so we can check the current version and try to update manually.
Do you need more help with this?