1. The sending State must make certain that the agrément of the receiving State has been given for the person it proposes to accredit as head of the mission to that State.
2. The receiving State is not obliged to give reasons to the sending State for a refusal of agrément.

I was interested to find that recieving states had this right. (Although the traditional 19th century response to small countries was to deploy a gunboat and shell the palace till the locals agreed)

Theres always the option to break off diplomatic relations, after all it's not a real state. and its usually not allowed for a states representatives to interfere with the internal politics of a state, as the catholic church tends to do in preaching about contraception and abortion, it could be argued that there are grounds (And other countries have been bombed for far less)

Any idiot can face a crisis - it's day to day living that wears you out.