Thanks for your question. There are probably several ways to address the problem, but here is a suggestion on how to tackle it.
The question we are trying to solve is how do we increase the volume of subscribers?
Of course if you have a case like this in an interview, first try to understand the ultimate objective (does it really matter to have more people subscribe if we can not retain our subscribers for more than 2 months? Is there any hidden issue?)
If there is nothing else, I would look at it as any other volume case. I would highly recommend to first try to structure in a MECE way the universe of possible solutions to grow the subscriber base, by building an issue tree. For example, growing the subscriber base is either :
A) Attracting subscribers :
(i) which customers (segment breakdown by age, geography, etc),
(ii) what offer and value proposition (pricing, content)
(iii) what marketing strategy:
- marketing budget
- marketing channels (content per channel)
or B) Retaining subscribers : improving the user experience along the key customer journeys
(i) Onboarding : ease of sign up and KYC
(ii) Looking for a content (ergonomy of the platform, size of the font, colors used, etc)
(iii) Viewing experience
(iv) customer support
And on each lever try to understand what differentiates our target segments from other segments (e.g. marketing via social networks may not be the most efficient/effective ; content strategy will likely need to be adjusted for seniors), and have an idea on how you could get that information (expert interviews, focus groups, etc).
Again there are probably other ways to look at this problem, but in any case you should strive to have a structured approach in a MECE way.
I hope this helps. Let me know if you would like to exercise your structuring skills, happy to dedicate some time.