Hi @science-physicist-94! Welcome to Postman community 
As @odanylewycz suggests, request body cannot be modified in script - here is a similar question discussed: Update request.body in pre-request script
Hope this helps!
Hi @science-physicist-94! Welcome to Postman community
As @odanylewycz suggests, request body cannot be modified in script - here is a similar question discussed: Update request.body in pre-request script
Hope this helps!