Invalid discriminator

Hello, I try to read modlist of a player from spigot.

So I read the doc of FML2 handshake, now I know I have to send

- -2 as byte to do a handshake reset

- 0 as byte ; 2 as byte ; 1 as int to do a serverHello

Then wait the client's response.

But in the client console

�[m�[1;31m[19:14:22] [Render thread/ERROR] [ne.mi.fm.ne.si.IndexedMessageCodec/SIMPLENET]: Received invalid discriminator byte 254 on channel fml:handshake
�[m�[33m[19:14:22] [Render thread/WARN] [minecraft/ClientPlayNetHandler]: Unknown custom packet identifier: fml:handshake
�[m�[1;31m[19:14:22] [Render thread/ERROR] [ne.mi.fm.ne.si.IndexedMessageCodec/SIMPLENET]: Received invalid discriminator byte 0 on channel fml:handshake
�[m�[33m[19:14:22] [Render thread/WARN] [minecraft/ClientPlayNetHandler]: Unknown custom packet identifier: fml:handshake

An idea ?

Thank you a lot.