Transfer Order number for Production order

Hi,

what is the best way to get the transfer order number (LTAK-TANUM) for picking for a production order?

Picking can occur first in IM (via MB1A for example) or in WM (via LP10). Requirement Tracking Number cannot be used as it has only a length of 10 characters (production order number up to 12 characters).

Reservation number (LTAK-RSNUM) is only filled in case picking is done from IM first.

Cheers

Mathias