I turned down a job offer, the hiring manager wants to meet up. Why? Should I?

So I applied to this Junior Data Scientist position at a startup (not necessarily looking to change jobs, but always be applying, right?). After 4 interviews and two technical tests they eventually gave me an offer I accepted. When I went to give my two weeksI had the chance to talk with my manager about my future in the company and they offered a raise, a promotion, an extra monthly bonus and the chance to be more free to decide …

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