When traveling in Oxenfurt, you will be approached by two Redanian soldiers asking for a "war tax." They can be found under the archway leading from the Oxenfurt Harbor signpost to the marketplace. You have two options:
Option 1: Pay Them Edit
This will cost you 50 . You can them find them a few days later, loitering at Oxenfurt’s south gate. They will again ask for more money, and you again can choose to pay them (again) or refuse. If you pay again, you'll never see them after this, but if you refuse, you may run into them on the outskirts of Oxenfurt a few days later. They will be angry at you for getting them in trouble. You can choose to fight them with your fists or kill them with your sword. The quest will then end.
Option 2: Refuse to Pay Edit
They will call their superior and accuse you of being a spy. The superior will not take the bait and will threaten to send them straight into battle for extorting money. The quest finishes and you can be on your way. After some time, they can be encountered again east of Novigrad gate (right next to two houses, close to the quest The Most Truest of Basilisks). You will be able to use axii, pay them 50 crowns, or fight them (But beware! They have stats of guards, therefore, the fight will be very tough!)