If the one who swears an oath says “In sha Allah,” he will not be breaking his oath (if he does not fulfil it) and he does not have to offer expiation. The same applies to vows.

Calling on Allah to bear witness that one will do or will not do something comes under the ruling on oaths, if it was intended as such. So if you intended to swear an oath when you said that, then it is an oath, and you may accept the money and offer expiation for breaking your oath. See the long answer for more details.