荷物自体はさくっと発送済みなんだけど、その旨/意図を伝える前に

「I already made the payment, please confirm it. Thank you!」と先手を打たれた

ので、例文と検索結果のこぴぺを交えて自分なりにアレンジしてみますた；

Hello, Mr/Ms.FULLNAME

I'm sorry I didn't reply to you sooner.

I had sent the parcel at September 29(in Japan, GMT+9).

If you want to confirm, please see my public space on Windows Live SkyDrive.

I uploaded some pictures of the package and receipt:

https://skydrive.live.com/****************************

I hope you will receive the parcel without any problems. Thanks for your bid again.

P.S.

I'd like to mention that to you, though you may know already:

Sending cash(both bills and coins) by regular postal mail is ILLEGAL in Japan,

so it is usually very hated and refused.

For the future, you might find out about other options to send money to Japan beside Paypal.

(For example, Net-Banking, International-exchange, and so on)

You can take it or leave it, but here's a piece of advice for you.

…末尾の「老婆心ながら忠告しておきます」的なニュアンスでツンデレ風味を演出してみたつもり(ばか)