Hi there,

I tried your modification and it didnt change my case.

I use
perl v5.14.2
LWP::UserAgent v6.06
HTTP::Request v6.00
IO::Socket::SSL 1.955

Adding

use Net::SSLeay;
$Net::SSLeay::trace = 2;
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as suggested on stackoverflow : http://stackoverflow.com/questions/26732578/500-error-with-lwpuseragent produced the output

DEBUG: .../IO/Socket/SSL.pm:449: socket not yet connected
DEBUG: .../IO/Socket/SSL.pm:451: socket connected
DEBUG: .../IO/Socket/SSL.pm:469: ssl handshake not started
DEBUG: .../IO/Socket/SSL.pm:504: using SNI with hostname sis-t.redsys.
+es
DEBUG: .../IO/Socket/SSL.pm:527: set socket to non-blocking to enforce
+ timeout=10
DEBUG: .../IO/Socket/SSL.pm:550: ssl handshake in progress
DEBUG: .../IO/Socket/SSL.pm:560: waiting for fd to become ready: SSL w
+ants a read first
DEBUG: .../IO/Socket/SSL.pm:570: handshake failed because socket did n
+ot became ready
Error: 500 Can't connect to sis-t.redsys.es:25443
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