Hello Ankur,
what you described regarding the absence of value for Requester attribute search result is "normal".
This is the same for me...
You have to put directly values:
O 50000010 for organizational unit (with space between object type and object ID),
USTATA for user (with no space).
What Kiran is talking about is only for team purchasing substitution: no link with Shop on-Behalf.
Regards.
Laurent.