FastLED: "Invalid pin specified"
I think what @IgnacioVazquez-Abrams is getting at is:

void setup() {
  FastLED.addLeds&lt;WS2812B, LEDCOUNT&gt;(leds, LEDCOUNT);
}


Has LEDCOUNT showing up for both the number of LEDs and the data pin identifier.

Try:

void setup() {
  FastLED.addLeds&lt;WS2812B, DATAPIN, GRB&gt;(leds, LEDCOUNT);
}


This puts DATAPIN in the right place, and also adds the color order typical for WS2812B, GRB