I removed the username and password from the JSON request so it was sending a blank object and it brings back the same error as you are receiving.
You need to add a JSON body to the request with a username and password.
Set up a new user: Find the following request in the The Good Bank APIs collection, and duplicate it over to the Setup folder.
POST Create User
Under the Body tab, update the username and password of your new user. Make a note of this information using any method you prefer. Hit Send to create a new user. The response will contain a user_id. Create a collection variable called user_id with this information, using any method you prefer.