It seems that FastLED.h lack of some developper to get it working properly on ESP32 now. I jumped to AdaFruit NeoPixel lib and run this sketch successfully using your PIN values. #include <M5Core2.h> #include <Adafruit_NeoPixel.h> #define LEDBAR_PXL 10 #define LEDBAR_PIN 25 Adafruit_NeoPixel ledBar(LEDBAR_PXL, LEDBAR_PIN, NEO_GRB + NEO_KHZ800); void setup() { M5.begin(); // put your setup code here, to run once: ledBar.begin(); ledBar.show(); } void loop() { // put your main code here, to run repeatedly: ledBar.fill(0xFF0000); ledBar.show(); delay(750); ledBar.fill(0x000000); ledBar.show(); delay(500); }