mySerial' was not declared in this scope

This error message usually appears in C++ programming when you try to use a variable or function that has not been declared or defined in the current scope or program.

To solve this error, you need to make sure that the variable or function you are trying to use has been declared or defined before you use it. This can be done by including the appropriate header files or by declaring the variable or function at the beginning of your program.

In this particular case, it seems that the variable `mySerial` has not been declared in the current scope. To fix this error, you can try declaring the variable before using it. For example, you can add the following line of code at the beginning of your program:

Serial mySerial;

This will declare a variable named `mySerial` of type `Serial`, which you can then use in your program.