No option for payment information

Firstly, I am part of my sister's family sharing and she's the organizer. I got a 7-day free trial for Duolingo but before i can access it, I was redirected to a place where I'm supposed to put my card details, but it's blank. There's no option for that. I attached a photo below. This is surprising seeing as I've been able to use my sister's card information to access free trial period on some apps and it has worked. Idk why this is happening. Please suggest possible reasons why this is happening.