BLF then pickup does not work

I am trying to monitor extensions (BLF) and pick up the extension that is ringing.
Now the extension can succssfully moitor another extension.
When the display show ringing, I pressed the extension and try to pick up.
The extension displays “603 declined”.

I would like to implement the function with using the replaces header
as says.

Does anyone know how to configure in Asterisk?(Asterisk 1.8)