Wait for the compilation progress bar to complete. Once finished, the message "Upload Finish" will appear, and the LED on your physical board will begin blinking. Troubleshooting Common Issues in v3.4.12
Below is a guide on how to actually create or "put together" a custom feature (function) in mBlock 3.4.12. 🛠️ Creating a Custom Feature (Block) in mBlock 3.4.12 mblock 3.4.12