I'e been banging my head against this bulk rename for Meraki APs for a while, and found your post. Could you please share complete Postman steps you went through? You can PM me at troy.reppert@corebts.com.
I like you have been able to use the put command to make single changes, just couldn't get a csv file to pass variables. I've also started working with JSON file to try to make the change. Been working through the same docs as you, just keep getting the 404 error.
Thanks