All perfect praise be to Allah, The Lord of The Worlds. May His blessings and peace be upon our Prophet Mohammad and upon all his family and companions.
Based on the details of the transaction given above, this is an exchange contract. In this contract, the exchanged currencies must be equal in amount. The evidence on this is that Narrated Ibn Shihab: that Malik bin Aus said, "I was in need of change for one-hundred Dinars. Talha bin 'Ubaidullah called me and we discussed the matter, and he agreed to change (my Dinars). He took the gold pieces in his hands and fidgeted with them, and then said, "Wait till my storekeeper comes from the forest." `Umar was listening to that and said, "By Allah! You should not separate from Talha till you get the money from him, for Allah's Messenger (Peace be upon him) said, 'The selling of gold for gold is Riba (usury) except if the exchange is from hand to hand and equal in amount, and similarly, the selling of wheat for wheat is Riba (usury) unless it is from hand to hand and equal in amount, and the selling of barley for barley is usury unless it is from hand to hand and equal in amount, and dates for dates, is usury unless it is from hand to hand and equal in amount." {Related by Bukhari}.
In order for the exchange contract to be considered valid, both items must be of the same kind and the exchange is done on the spot in the same sitting. This is whether the collecting was actual or constructive where the amount is credited to the account of the other party directly.
Resolution No. (55/4/6) of the International Islamic Fiqh Academy stated, "Some forms of constructive collecting considerable in Sharia and custom/habit:
1- Crediting an amount to the account of a customer in the following situations:
A-If a certain amount is credited to the customer`s account directly or via bank transfer."
In conclusion, you (Asker) aren`t allowed to exchange (100 JDs) for (97 JDs) since this is considered excess usury that Sharia prohibits. And Allah the Almighty knows best.