Can not get success when setting MIME tye whithin HTTP GET when using vco REST API

Hi:

   When I set accept header in http, server return bad request. If I don't set accept header, it will be success.

send: 'GET /vco/api/workflows HTTP/1.1\r\nAccept-Encoding: identity\r\nAuthorization: Basic dmNvYWRtaW46dmNvYWRtaW4=\n\r\nHost: 9.111.254.58:8281\r\nConnection: close\r\nAccept: application/json;v=5.1.1\r\nUser-Agent: Python-urllib/2.6\r\n\r\n'

reply: 'HTTP/1.1 400 Bad Request\r\n'

Anybody can tell me where is the worng?