Failed to download imageset zipfile, need help

[robbine]

I tried to download a dataset using python script like this:
./imagetagger_dl_script.py 8
however response's status code was 411 after calling requests.get method.
I also print out response.request.headers ,here is the content of headers
{'User-Agent': 'python-requests/2.27.1', 'Accept-Encoding': 'gzip, deflate', 'Accept': '/', 'Connection': 'keep-alive', 'referer': 'http://172.31.243.123:8000/', 'Cookie': 'sessionid=fky9jdsmrbn8eokmcd04jcrwuikb1pvl', 'Content-Length': '117', 'Content-Type': 'application/x-www-form-urlencoded'}

By the way, here is my request:
GET /images/imageset/8/download/ HTTP/1.1\nUser-Agent: python-requests/2.27.1
Accept-Encoding: gzip, deflate
Accept: /
Connection: keep-alive
Referer: http://172.31.243.123:8000/
Cookie: sessionid=hueyfk68nm56mbisn34nribeajhnz0v5
Content-Length: 117
Content-Type: application/x-www-form-urlencoded
Host: 172.31.243.123:8000