This error message is caused because you don’t have the ICACHE_RAM_ATTR attribute in the name of your interrupt service routine (ISR) function. So your pulseCounter ISR name should look like this:
void ICACHE_RAM_ATTR pulseCounter()
When you do this, you’ll probably find that you get a compiler error message that says something like "pulseCounter was not declared in this scope. You fix this by moving your pulseCounter IRS above your void setup in your sketch.
As you now have three reasonably active topics that are all about the same project, I’m going to lock this topic and one other, and ask that all future posts are made in the following topic…
Pete.