#-- everything from the FORM here (nerver use colons here):
my@form_fields= (  csrf_token                        => $csrf_token,
                      #-- above looks right, according to form example
                   subscribees                       => "$name <$email>",
                   setmemberopts_btn                 => 'Submit Your Changes',
                   send_notifications_to_list_owner" => "1"
                );

#-- read the API-doc: IF the csrf_token is required in the header
#   (use colons to prevent canonicalisation):
my @headers =   ( ':csrf_token'                      => $csrf_token,
                  ':member_verbosity_threshold'      => 0,
                  'User-Agent'                       => 'Mozilla/5.0'
                );

my $res = $ua->request(POST $_[0],
                       @headers,                    
                       Content => \@form_fields
                      );