Zscaler Operations Engineer interview questions

Interviewed over a period of about 3 weeks with 4 separate upper management/executives including the owner, and 1 engineer. Each interview on a separate day. Interviews were conversational dialogue, questions and answers, and explanation of the products. Was given offer letter, then suprisingly after I accepted, was told a few weeks after starting work that I need to complete background check also (the manager forgot to do this before the formal offer was given.)