I understand schedulers have to deal with reams of e-mails daily. So I always put something in the subject line, and I keep my request polite, to the point, and short.
"I asked for a bonus of $35 on this shop, and was told that would be OK. The fee was $12, a $35 bonus would total $47, but the shop is in my log at $35. Could you fix this before I go do the shop, please?"
If I don't get a reply within, say, 24 hours, I resend the same e-mail, with in the subject line: May I have the courtesy of a reply?
If it's a difficult scheduler (they do exist!), I might add "I'm terribly sorry, but if this isn't fixed, I'll have to cancel the shop, as I cannot do it for $35". But I think I've used that threat only 2 or 3 times in ten years. And only with one scheduler, who is VERY difficult.