@thienlam your code has been removed, as you haven’t edited your post to add triple backticks, which are necessary for the code to display correctly on the forum.
When I said to you previously that you should…
I did that for a good reason. It’s disappointing that you haven’t taken my advice onboard.
From what I can see from the limited amount of information that you have chosen to share, you’re putting yourself at a distinct disadvantage by using the serial port on your board for communication with your PZEM instead of creating a SoftwareSerial port for that purpose.
You’re probably also screwing-up that PZEM communication by sending serial print data to the port your PZEM is connected to.
You might be better looking at some of the other PZEM projects that have been posted on this forum instead of continuing down the route that you are currently following
Pete.