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Select the port of your D1 Mini from the Tools > Port menu. If that menu is grayed out or the port of your Arduino board is not shown then one of the following may be the cause:You may need to install the driver for the USB-serial chip on your Arduino. Determine which chip is used on your Arduino and install the driver.You may be using a charge-only or defective USB cable. Test your cable on another device to confirm that it works for data.Using a USB 3.0 port on your computer may cause problems. Try a USB 2.0 port or use a USB 2.0 hub plugged into your USB 3.0 port.