Well, the thing is, there are kind of a lot of them.
Nerosyan could send their funding late. Nerosyan could send less funding than they're supposed to. Whoever's bringing the money could be ambushed by demons that snuck through the barrier, or really well-organized bandits, or some kind of auromvorax hybrid that can live this far north. (Digression into an argument about whether auromvoraxes are actually real.) There could be a blizzard that slows them down. If he had it teleported instead, they'd be using Mendev's very limited teleport capacity, and the teleport might still go off-target, or the teleporter might decide to just take it and fuck off to the Stolen Lands or something (in the Stolen Lands theft is legal so no one would stop them, that's why they're called the Stolen Lands). (Digression into a very one-sided argument with someone who doesn't believe teleporters are real.)
Whoever set the budgets might have underestimated the amount of money they would need to spend on food or weapons or equipment repairs, and take from the money for paying the soldiers in order to compensate, or vice versa. Some of the money might be intended for specific border forts, does he get to order the border forts to do something different? There might be some kind of emergency that's really expensive to fix such that money needed to be redirected from somewhere in order to compensate. Someone might be filling holes in the budget with donations from some specific person of means and that person could die and leave everything to their less-charitable children. In theory they pay casters more if they're higher-circle and that could mess things up if people circled up quickly enough. Someone might just skim off the top because they're greedy or a cultist, why else would they be stealing from Mendev?
(They can continue in this vein for as long as he likes.)