HUs in Inbound delivery

Hello Experts

Business requirement is to capture the Tracking number (alpha numeric, length 20 char) from the external system in inbound delivery.

to simulate the scenario, I'm trying to enter the value manualy in field VEKP-INHALT in Inbound delivery creation transaction. but system is not accepting the value, no error is shown, the entered value just disappears.

INHALT Description of Handling Unit Content

Could you pls let me know the means of entering the value in the above mentioned field or are there any other fields in Inbound delivery where i can capture the tracking number which supports idoc as well.

Thank you.