||You probably mispelled or miscapitalized a command or variable name. Common examples include:
- 'pinmode' → pinMode (the M must be capitalized)
- 'digitalwrite' → digitalWrite (the W must be capitalized)
- If you declare a variable as redLED, then you must always refer to it the exact same way. redled or redLed will result in this error.
- Every letter in the Arduino constants used to set pins HIGH and LOW must be capitalized.