Then I tell the client that I sent him the API specification 2 months ago. If he isn't happy with it, he can write a wrapper himself.
Of course, I could also change the API. Whether or not I do that depends on 4 factors in that order:
0) Do I have the time and resources to do so?
1) How important is the client?
2) How much does he pay me to do the change?
3) Exactly how annoying is the client?
Then I tell the client that I sent him the API specification 2 months ago. If he isn't happy with it, he can write a wrapper himself.
Of course, I could also change the API. Whether or not I do that depends on 4 factors in that order:
0) Do I have the time and resources to do so?
1) How important is the client?
2) How much does he pay me to do the change?
3) Exactly how annoying is the client?