Is 请扫我的 an appropriate way ask the cashier to scan my phone for payment?
清扫我的
  qīng sǎo wǒ de  


Has a few issues.


please is 请 qǐng and not 清 qīng
的 de is unnecessary here


请扫我 is okay but you're mostly likely leaving out essential information for the other person involved.



The person in charge of ringing you up usually wants to know if it is WeChat or Alipay that you are using. I believe they need to key something in on their registers before scanning you, I'm not totally sure but it always looks that way. The better way to aid the interaction would be for you to directly tell them method of payment you will be using. After they tell you the amount owed you can just say something like


好，支付宝哈
好，微信哈


Or you can change 哈 to whatever modal is popular in your vicinity.