Expedia SSE-ML — open-ended HR workflow design round; reject

How would you go about a workflow designed for the HR operations where tasks like one has to send sms or emails to employees when may be a public holiday is declared or may be a notice has to be published or even salary slips has to be send. The ops team has to get user/employee details before sending the sms/email. What are you thoughts?

PS: I tried to dig up upon the requirements and try to figure out the expectation. I asked if the expectation was to design a system? But the interviewer said consider you have this requirement what would you do? I went ahead and designed a system using LLD and the interviewer end the interview 15 min early. I was rejected so I am sure that was not what the interviewer was looking for. Any inputs on what should I have done to approach this?