On Altivars, in order to send TUN via communication channel in Cia402, you need first to go to operation enable state.

Sequence to launch the TUN on ATV320/ATV6xx/ATV9xx/ATV340
1.    Power ON the drive. Drive displays NST and drive state is “Switch on disabled”
Here the drive has to go into operation enable, but without motor movement, because if the motor is started, the TUN cannot be done. To do this, we respect the same sequence as in older drives ATV312 or ATV71, but with activating bit 8 of command word CMD , that is “halt” bit
2.    So to go into operation enable but not start the motor you need to send the CMD sequence according to CIA402 as 0x0006 --> 0x0007 --> 0x010F
3.    The drive goes in operation enable (display RUN but not start)
4.    Then you can write TUN=YES via the SDO
5.    The TUN is done
6.    To start, just remove the “halt” bit : CMD = 0x000F