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Please follow the advice given in the link below when posting code, in particular the section entitled 'Posting code and common code problems'
Use code tags (the < CODE/ > icon above the compose window) to make it easier to read and copy for examination
https://forum.arduino.cc/t/how-to-get-the-best-out-of-this-forum
In my experience the easiest way to tidy up the code and add the code tags is as follows
Start by tidying up your code by using Tools/Auto Format in the IDE to make it easier to read. Then use Edit/Copy for Forum and paste what was copied in a new reply. Code tags will have been added to the code to make it easy to read in the forum thus making it easier to provide help
Which Arduino board are you using ?
please, please never ever again post pictures of text... Not only they are not readable nor usable directly for copy&paste but they use up lots of storage and internet bandwidth which contributes to polluting the planet.
➜ do your part and do yourself a favour and please read How to get the best out of this forum and modify your post accordingly (including code tags and necessary documentation for your ask).
which arduino are you using ?
Ok. I will never again post picture again. I am using Arduino Uno and ESP32 WROOM however I dont think that promlem is occur because of my arduino boards.
Thanks for helping. Pictures are fine when they are not just text you could copy and paste.
do you get the error message when you compile the sketch with the UNO selected as the target platform?
No. Actually I dont use any board, I just test it with the verify button.
Which board have you got selected in the IDE when you do the verify ?
It was ESP32WROOM-DA Module.
I am sorry for taking your time and thank you trying to help me. It works when I install ESP32SoftwareSerial librarry.
Kind regards.
no problem - we are here voluntarily to help out 
SoftwareSerial is available by default if you use the UNO but it's not available (and usually not needed) by default for the ESP32 and thus you would need a custom library.
The ESP32 has multiple hardware UART, so you could use Serial1 or Serial2 rather than using a Software emulation... it will be more robust.
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