Difference between a buyer and a buy planner?

In a department store, a buyer and buy planner make the buying decisions for a specific department.

I am confused on the roles of each and can't find much online.

I thought buy planner would be the first you talk to, but every time I talked to a colleague of their's, they push me to the buyer and give me the contact of the buy planner additionally.

Anyone have any experience how these two work together?