What??? Are you inventing new Blynk functions or something? I think you need to reread the Documentation and look at some Examples before reinventing the wheel
You don’t add any underscore & number to a function command, each one is already identified by the vPin used.
BLYNK_WRITE(V2){
// do stuff here when widget attached to V2 is processed
}
BLYNK_WRITE(V3){
// do stuff here when widget attached to V3 is processed
}
BLYNK_WRITE(V4){
// do stuff here when widget attached to V4 is processed
}
PS - the approved and better looking way to format posted code in this forum is also in the Documentation