Delete Subscriber doesn't work

I’m trying to delete a user as part of a UI test flow and I’m using this API - https://www.revenuecat.com/reference/delete-subscriber

After entering my V1 api secret token and the user I want to delete’s ID, I get the following bas script

curl --request DELETE \
     --url https://api.revenuecat.com/v1/subscribers/my-user-id \
     --header 'accept: application/json' \
     --header 'authorization: Bearer sk_token'

This however returns just

{"code":7227,"message":"Content-Type not application/json"}

My token is for V1 of the API and the user id is right, I’m not passing in any JSON.

Why am I getting this error?