Hey!
Congratulations on the interview invite!
I would personally start by giving it your best shot and talking through anything you do know about the topic, even if it is only quite broad. Often, the interviewers are just as interested in seeing how you approach an unfamiliar commercial issue, and I think it would be unlikely that they'll expect you to have in-depth and detailed knowledge on everything that could come up.
If you then reach the limit of what you know, I think it is absolutely fine to be honest about that rather than trying to bluff. You could say something along the lines of "I'm not too familiar with that specific topic yet, but I'd be really interested to learn more about it". Then, I'd make sure that you stay engaged by asking questions and respond to any extra context they give you that might nudge you in the right direction.
Generally speaking, I think a thoughtful and curious discussion usually comes across much better than trying to force a perfect answer. As @WillKitchen stated, even finding ways to link it to things that you are confident speaking about will show that you understand where it fits in the wider context and how it impacts other areas.
Best of luck with the interview!!
if anyone needs advice, please PM. Happy to help and prevent others from embarrassing themselves like I just did 
