Short answer

Your T-bill allotment value is lesser because T-bills are issued at a discount to their face value and redeemed at full value upon maturity.

How T-bills work

T-bills do not carry an interest component, which is one of the biggest differences between T-bills and bonds. Instead, T-bills generate returns through the discount pricing mechanism.

Example

The face value (also called par value) is ₹100. This T-bill is issued at a discount to its par value, say ₹97. After 91 days, you will receive ₹100, earning a return of ₹3.

This discount structure explains why your allotment value on Arrow appears lesser than the par value of ₹10,000 (or multiples of ₹10,000).