بسم الله الرحمن الرحيم
(1) If the purchasing is rejected by the concerned department without any reason then it is a kind of injustice from their side. You may give them something as a gift in order to save yourself from their injustice. In this case you shall receive no sins.
(2) If that person gives you the order or contract for himself and he is not a wakil from any other person then as per approbation it is lawful to give him something as gift or cash or arrange his stay in any hotel etc.
Allah knows Best!
Darul Uloom Deoband