I am developing an app that uses material (the material I want to show is a website) which is licensed with CC BY-NC-SA 3.0 but I want to place ads in my application. The application has another functions other than showing the content. I thought that if I keep the links for the content and open it in a webview inside my app (yes it connects to the server) there would not be a problem. Also, I thought I can put a premium option that no ads will be showed and the content will be stored locally then will be shown in a webview because I'm not generating any profit from it. Would this violate the license ?
I'd consider that a license violation to use CC BY-NC licensed material in such way. The CC BY-NC license says already in its name that the licensed content must not be used in commercial context.
There exist a study from CC which gives general interpretation of the NC clause as
On a scale of 1-100 where 1 is “definitely noncommercial” and 100 is “definitely commercial” creators and users (84.6 and 82.6, respectively) both rate uses in connection with online advertising generally as “commercial.” However, more specific use cases revealed that many interpretations are fact-specific. For example, creators and users gave the specific use case “not-for-profit organization uses work on its site, organization makes enough money from ads to cover hosting costs” ratings of 59.2 and 71.7, respectively.
Reasoning could be as follows: if this usage is allowed, then one enters a slippery slope and can simply use it for any advertizement, decoration or similar in any context as long as it is not sold itself. It's the impression the user has to get (it's used to promote content which aims to make a profit), not the technical means used to dispay a CC BY-NC license piece of art. It's different if you use the art and ask for donations for the combined work.
This is not a legal interpretation but just what people who use it mean and interpret it. You might simply approach the artist and explain the situation and your intentions - and ask for permission. You might also seek legal councel. Legal interpretation will vary depending on your jurisdiction.