> ... sis-t.redsys.es:25443

This server has some serious issues. If you use the old default cipher set of IO::Socket::SSL, that is "ALL:!LOW", with TLS1.0 or higher the connection simply hangs. This kind of problem is often seen in connection with older F5 load balancers in front of the server, which simply drop ClientHello packets greater than 255 bytes. Since version 1.962 (about a year ago) IO::Socket::SSL will use a smaller (and more secure) cipher set to work around such problems. But I guess you are using an older version of IO::Socket::SSL.

Crypt::SSLeay instead uses the default cipher set of OpenSSL, which makes the packet in this case just 248 bytes and thus small enough. That's why it works with Crypt::SSLeay. But please note, that Crypt::SSLeay does not make any verification of the hostname against the servers certificate and is thus open to man-in-the-middle attacks.

With current versions of IO::Socket::SSL the problem should be fixed too. But, since you are using a proxy you should use the latest versions of LWP::UserAgent and LWP::Protocol::https too, because proper proxy support with IO::Socket::SSL backend was only added to version 6.06 (it might be in 6.04 already if you use Debian or a spinoff like Ubuntu).