System design for a pharmacist organization system [closed]

Problem Statement:

design a class pattern for the following requirements:

A pharmacist writes prescription to people. A cashier collects cash and returns cash to pharmacy. A Manager manages employees. A Manager can sometimes work as a cashier and a pharmacist

I approached the design implmentation on Java with interfaces and java classes, after which I guess the interviewer was not that satisfied with the approach.

Followup: How would the design should be implemented if there are 100 managers/employees and each of them have different jobtypes. For example - the current manager had 1 job roles to manage employees and 2 partial job roles i.e of cashier and of pharmacist.

I was not able to come up with the design and will appreciate the help from the community to get an approach to think better for these types of problem statement and also deal with scalablity when considering to scale system.