Later I noticed there was an option for a 10% discount on my coach ticket
It was only Later I discovered a 10% discount option for my ticket
I later realized that my online coach ticket had a 10% discount option
It was only Later I discovered a 10% discount option for my ticket' is often more a formal and polite way of saying about the realization of finding out there was a discount later on.
'I later realized that my online coach ticket had a 10% discount option' is also a polite and formal way of expressing that 'I'd noticed later that there was a 10% discount option'
'Later I noticed there was an option for a 10% discount on my coach ticket' is more of a easier and common way of expressing this, more commonly and widely used.
It was only Later I discovered a 10% discount option for my ticket'（10％引きになるオプションがあることに後で気が付いた）
= フォーマルで丁寧な言い方です。割引があることに後になって気が付いたと言っています。
'I later realized that my online coach ticket had a 10% discount option'（後になって、オンラインで買ったエコノミーのチケットに10％引きのオプションがあることに気が付いた）
=「後になって10％引きのオプションがあることに気が付いた」の丁寧でフォーマルな言い方です。
'Later I noticed there was an option for a 10% discount on my coach ticket'（後になって、オンラインで買ったエコノミーのチケットに10％引きのオプションがあることに気が付いた）
= これはより易しい一般的な言い方です。広く一般的に使われる言い方です。
After buying the ticket, I noticed there was a 10% discount option
If you buy a ticket and then later notice there was a discount option which you could have used at the time of purchase, it is, to say the least, a little annoying.
The sensible thing to do would be to return to the place of purchase and point out that it was just an accident that you didn't apply the advertised discount and could you please have a refund? You may follow up the above phrase with:
"Would it be possible to apply this discount retrospectively and refund me the difference?"
チケットを買って後から購入するときに使えばよかった割引オプションに気づいたとき、ちょっとイラっとしますよね。
そのチケットを返して、割引でない方を間違って買ってしまったと言うといいと思います。
Could you please have a refund?
払い戻ししてもらえますか？
"Would it be possible to apply this discount retrospectively and refund me the difference?"
割引を適用して、差額分を返金してもらうことは可能ですか？
I saw the discount option after I had already booked my ticket.
"I saw it too late." This explains that you did see the discount option but you had already booked your ticket so it was too late.
"I saw the discount option after I had already booked my ticket." This explains that you first booked your ticket and only after that did you see the discount option.
"I saw it too late."（後から見た）
これは割引の選択があった事は分かったけど、すでにチケットは購入済みだった、と言う事を説明しています。
"I saw the discount option after I had already booked my ticket."
（チケットを買った後に割引がある事に気が付きました）
これはまず最初にチケットを購入することしか考えていなかったので後になってディスカウントの選択があった事にきがついた、と言う事を説明しています。
I noticed later that there was a 10% discount offer
After I bought it, I noticed the 10% discount offer
If you notice something after you have done something then you can say 'i noticed later' or 'after I bought it, I noticed'
if a company offers a 10% off something then this is often called a '10% discount offer'
あることに何かをした後気が付いたなら、
'I noticed later'（後で気が付いた）
や、
'after I bought it, I noticed'（買った後気が付いた）
と言えます。
会社が10％の割引を提供するなら、これはよく '10% discount offer'（10％割引）と呼ばれます。
Only after purchasing this ticket did I notice that there was an option for a 10% discount.
There was a 10% discount I didn't use, I only realized after buying the ticket!
We can get so busy that our minds are full, we tend to forget even the simplest of things.
When we make this mistake we can rectify it by returning to the sales department and explaining our mistake, if they are kind enough you may get a refund.
We can simply explain to them that we realized too late, after purchasing the ticket.
After purchasing the ticket, I realized there was a 10% discount offer.
I booked my ticket before realizing there was a 10% discount offer.
I booked my ticket before realizing there was a 10% discount offer.
After purchasing the ticket, I realized there was a 10% discount offer.
I realized the discount too late! I had already bought my ticket.
I booked my ticket before realizing there was a 10% discount offer.（チケットを予約した後、10％割引のオプションがあるのに気が付いた）
After purchasing the ticket, I realized there was a 10% discount offer.（チケットを買ってから、10％割引のオプションがあるのに気が付いた）
I realized the discount too late! I had already bought my ticket.（割引に気付くのが遅すぎました。もうチケットを予約してしまっていました）
It wasn't until after I bought the ticket that I saw that there was an option for a 10% discount!
In American English, we commonly use "it wasn't until" to talk about noticing something after the fact. This sentence should also be easily understood by British English speakers. I hope that this helps :)
イギリス 
南アフリカ 
アイルランド 
アメリカ合衆国 
