This show is just gonna get better and better.
It could be that South Korea did not provide “agreement.” When the US proposes to send an ambassador to a country, it sends notification to the host country requesting their agreement on the person proposed. If they object, which is rare, then the nomination is withdrawn. It is reciprocal.
Agrément —
Diplomatic courtesy requires that before a state appoints a new chief of diplomatic mission to represent it in another state, it must be first ascertained whether the proposed appointee is acceptable to the receiving state. The acquiescence of the receiving state is signified by its granting its agrément to the appointment. It is unusual for an agrément to be refused, but it occasionally happens.