This error usually means the Arduino IDE can’t find the esptool utility required to upload SPIFFS data. To fix this, try these steps:

Ensure you have the latest ESP32 board package installed via Board Manager. Restart the Arduino IDE after installation or updates. Check your system PATH environment variable includes the path to esptool (usually inside the ESP32 package folder). If the problem persists, try reinstalling the ESP32 core or upload SPIFFS data using the command line with esptool.py directly.