あ、実は今日、会議があっているんですよ。

This as an answer for an invitation to do something today. Also the dialog I'm
talking about is over the phone.
CC BY-SA 4.0
2018-12-03T10:33:38.397
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2018-12-03T16:14:10.350
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question
grammar
Is the following sentence correct to decline a invitation?
If you're asking if this is the correct way to decline an invitation, then
yeah you can say that you have a meeting today as a way of saying "no I'm
busy".

If you're asking if your sentence is grammatically correct, then no, not
completely. While あっている is used in some dialects, it's not standard Japanese
so you should probably use ある.
CC BY-SA 4.0
2018-12-03T14:47:12.437
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answer
If you decline someone's invitation due to another plan such as a dialog.

In a formal way, you can say the following sentence.

"会議の予定が入っているため、申し訳ありませんがお断りさせていただきます。"

In a bit casual way, you can say the following sentences.

"あ、実は今日会議が入ってるんですよね。"

"あ、実は今日会議があるんですよね。"

Although this is a casual form, you can use this in the conversation with your
colleagues.
CC BY-SA 4.0
2018-12-03T16:14:10.350
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2018-12-03T16:14:10.350
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answer