Mr. White's first wish is fulfilled because he receives the money that he has wished for. For lack of anything more interesting, White ends up wishing for "200 pounds." This actually seems to be a pretty common wish for people without a more specific option: money. It doesn't sound like a lot, and indeed, even at the time of the story's writing it wouldn't have exactly been a fortune, but it would have been a nice sum of cash. Why not wish for a million? I don't know...he doesn't seem to want to be greedy. Of course, he doesn't think that paw will work, anyway.
Amazingly, he gets his wish, which also leads to the irony. It is ironic because he receives the 200 smackers as a settlement payment for his son's death. His beloved son has fallen prey to some nefarious industrial accident and his corpse has been pretty messed up in the process. "'He was caught in the machinery,' said the visitor at length in a low voice." The owners of the factory, admitting no liability or guilt, have decided to give the parents the 200 pounds as compensation.
Therein lies the irony. His wish comes true, and he gets the money, but at the cost of his son.
his wish was granted...because he got the money but he had to lose his own son,that died because of the fathers wish...so we learn that getting something might be on the cost of something else that might be more important.