blind transfer on 6731i

[tekilatex]

Hello,
I have a little trouble with aastra 6731i phone with
blind transfer.
I pick up my external call, then I press the button
transfer, call my No internal correspondent
then press transfer button to transfer my
appeal.
the phone start to ring intermittently as a reminder that the transferred call is
not answered. I think I missed a check mark somewhere.
Someone has an idea?

Thank you in advance
Teki