Good, it works for you, but I am not convinced, your program works as intended. Consider:

Token in HTTP-header (your current fix): 

my $res = $ua->request(POST $url,
                       'user-agent'                  => 'Mozilla/5.0',
                       ':member_verbosity_threshold' => 0,
                       ':csrf_token'                 => '2802000000...
+',
#-- not required:      'content-type'                => 'application/x
+-www-form-urlencoded',
                      );

[download]

Result: 

POST /xxx HTTP/1.1
TE: deflate,gzip;q=0.3
Connection: TE, close
Host: localhost:5000
User-Agent: Mozilla/5.0
Content-Length: 0
Content-Type: application/x-www-form-urlencoded
csrf_token: 28020000006.....
member_verbosity_threshold: 0

[download]

Token in HTTP-body (content) - this is more like what your <FORM ...> example would do: 

 my $res2 = $ua->request(POST $url,
                       'user-agent'                  => 'Mozilla/5.0',
                       ':member_verbosity_threshold' => 0,
#-- not in header:     ':csrf_token'                 => '28020000006..
+...',
                       Content                       => [ csrf_token =
+> '28020000006.....', ]  #-- but in body
                      );

[download]

Result: 

POST /xxx HTTP/1.1
TE: deflate,gzip;q=0.3
Connection: TE, close
Host: localhost:5000
User-Agent: Mozilla/5.0
Content-Length: 27
Content-Type: application/x-www-form-urlencoded
member_verbosity_threshold: 0

csrf_token=28020000006.....

[download]

Hope, that shed some light. I was also going to nitpick, that you should prepend your non-standard headers with 'X-' (like X-Csrf-Token), but that practise seems discouraged since a couple of years: SO: Custom HTTP headers : naming conventions. Thanks, I learned something new ;-)

In reply to Re^3: POST fieldnames with underscores by Perlbotics
in thread POST fieldnames with underscores by BernieC

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