hippo's advice is correct. Compare what you are sending against what you think you are sending.

See (for example) LWP::Debug for a good approach to see all the data you send:

use LWP::UserAgent;
my $ua = LWP::UserAgent->new;
$ua->add_handler("request_send",  sub { shift->dump; return });
$ua->add_handler("response_done", sub { shift->dump; return });

...
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