Catch traffic from mobile app (iOS/Android)

Hello,

even though I go through these steps: https://learning.getpostman.com/docs/postman/sending_api_requests/capturing_http_requests/
It is still not possible to catch traffic from native app (currently Iā€™m using iPhone). When I do the same with Fiddler (using FiddlerRoot certificate) - it works. What could be a problem? Do I need some certificate?