Creating a role for a package

I'm trying to add a role to an existing package in draft status. I'm getting

{
    "technical": "",
    "packageId": null,
    "messageLanguage": null,
    "messageKey": "http.status.415",
    "entity": null,
    "code": 415,
    "message": "Unsupported Media Type",
    "name": "Unsupported Media Type"
}

when posting the payload

{
	"signers":[
	{"email": "[email protected]",  
	"firstName":"firstName",
	"lastName":"lastName",
	"company":"default company",
	"title":"default title" 
	}
	],
	"name": "[email protected]'s role"
}

to https://sandbox.esignlive.com/api/packages/zYcg6ZoSuCzxYfunTy1hB03FXU0=/roles. I was trying to follow http://docs.esignlive.com/content/c_integrator_s_guide/rest_api/roles.htm#Create. Thanks, Jimmy