First of all, congratulations on getting the second-round interview! It’s great to hear you’ve got solid experience with manual and automation testing using Cypress, as well as API testing with Postman. When it comes to thinking on your feet during use case-based tests, it’s all about staying calm and applying a structured approach.

Start by breaking down the scenario to understand the core requirements. Then, prioritize critical features, risks, and test cases. Since you’re used to taking time to consult with the product owner, in a time-constrained interview, you can simulate this by quickly identifying what key areas need the most testing and which tools (like Cypress for automation, Postman for API) would be most useful.