They asked Case Studies on what parameters could be used for Machine Learning model, there were three rounds but in further rounds they asked theoretical Machine Learning based case studies.

2 rounds : Round 1 was talk about the ml models on my resume(went deep into their theory) and couple of case studies centered around amex's business model. Round 2 was case studies again and questions like why amex? both rounds were a mix of technical and hr.Would suggest strongly brushing up one's knowledge of credit cards and amex's revenue streams