how to fetch entire big ip configuration file

I tried to read 512 bytes but getting error back from bigip. Any idea what is wrong? also how do I completely read the file, like knowing filesize etc.

Request

GET https://172.18.20.98/mgmt/shared/file-transfer/ucs-downloads/bigipconfig.ucs HTTP/1.1

Content-Type: application/octet-stream

X-F5-Auth-Token: VOVJQUWKAPZ3AO4KGIY4BJDNJ2

Content-Range: 512

Host: 172.18.20.98

Response

HTTP/1.1 400 Bad Request

Date: 12 Jul 2019 07:53:37 UTC

Server: com.f5.rest.common.RestRequestSender

X-Frame-Options: SAMEORIGIN

Strict-Transport-Security: max-age=16070400; includeSubDomains

Pragma: no-cache

Cache-Control: no-store, no-cache, must-revalidate

Expires: -1

Content-Length: 0

Content-Type: application/octet-stream

Content-Range: 512

Local-Ip-From-Httpd: 172.18.20.98

X-Forwarded-Server: localhost.localdomain

X-Forwarded-Proto: http

X-Forwarded-Host: 172.18.20.98

X-Content-Type-Options: nosniff

X-XSS-Protection: 1; mode=block

Content-Security-Policy: default-src 'self' 'unsafe-inline' 'unsafe-eval'; img-src 'self' http://127.4.1.1 http://127.4.2.1

Connection: close