On WeChat Pay (微信支付) and Alipay (支付宝), 支付码 is the QR/barcode the customer shows for the cashier to scan. The reverse — the merchant's static QR you scan — is called 收款码 (shōukuǎnmǎ) 'receive-payment code.'
mistakes
Don't confuse 支付码 'code I show to pay' with 收款码 'code I show to be paid.' The same store wall might display both — the merchant's 收款码 for customers to scan, and the customer's 支付码 on phone.
