Using flask and restplus, how does one receive json in the body of get?

Question

A snippet from my flask app is like so:

scopes = api.model('Resource', {
    'scopes': fields.List(fields.String),
})

@api.doc(body=scopes)
    def get(self, account_id, pvp_type):
    ...

The sample body content that I supply on the swagger page is like so:

{ "scopes": [ "string" ] }

With the above, I get a response body like so:

{ "message": "Failed to decode JSON object: Expecting value: line 1 column 1 (char 0)" }

Please suggest what I might be doing wrong, Thx.