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you can have a tall size drink for free but if you choose venti size, you should pay 1,000 won for the size upgrade! but i guess you know it already?!

Oh really?? I didn't know that! They didn't take my card for payment so I guess I got lucky? kkkkk

OR they made you pay the upgrade and you didn't notice it!
You did somehow show your birthday coupon barcode, right?
then they can make you pay by the starbucks card registered on your account.
But still, that's weird if they didn't mention at all the extra charge...

You are right! I checked the receipt in my app and it shows 천원 payment -_-
Maybe they told me but I didn't understand ㅋㅋㅋ

ㅋㅋㅋㅋㅋㅋㅋㅋyou see!!! every size upgrade costs you 500 won! Venti means two times of upgrade so it costs 천원!

Haha I learned something new ! :) Is it the same for every drink? ㅋㅋ

Yeap. and every extra espresso shot costs 600 won, whatever the drink is.

Wow seems you are VVIP at starbucks haha :D Thanks for all the info!
I ordered my gold member card yesterday ><