Cybex Sirona help with forward facing

[Alixion]

Can anyone help where I might be going wrong converting the Sirona to forward-facing position?
I've followed the instructions and just can't see where I'm going wrong. It seems to be stuck only swivelling to rear-facing. Harness is clipped into red box, back kick-board thingy taken out, headrest is at maximum and forward-facing restraint cushion is buckled in.
I must be missing something!!!!