Starbucks Korea's estimated credit and debit card payment volume last month decreased by more than 10 billion won compared to the previous month. The downward trend in payment volume continues following the "Tank Day" controversy that occurred last month. According to Mobile Index by big data platform company IGAWorks on the 4th, Starbucks' estimated credit and debit card payment volume for May was tallied at 121.19 billion won. This is a decrea…