IIRC, it's
"col" => [ qw( KEYID CPUTYPE INSTANCE_ID SYSTEM_ID ) ]

What you had is the same as
"col", "KEYID", "CPUTYPE", "INSTANCE_ID", "SYSTEM_ID"
which is the same as
"col" => "KEYID", "CPUTYPE" => "INSTANCE_ID", "SYSTEM_ID"
which is obviously wrong.

Update: Confirmed.

LWP::UserAgent says:

This method will use the POST() function from HTTP::Request::Common to build the request. See HTTP::Request::Common for a details on how to pass form content and other advanced features.

HTTP::Request::Common says:

Multivalued form fields can be specified by either repeating the field name or by passing the value as an array reference.

so either of the following should work:

col => [ qw( KEYID CPUTYPE INSTANCE_ID SYSTEM_ID ) ]
[download]

col => 'KEYID',
col => 'CPUTYPE',
col => 'INSTANCE_ID',
col => 'SYSTEM_ID'
[download]