avrdude: stk500_recv(): programmer is not responding -HELP

Hi. I’m trying to upload a piece of code to my Arduino Uno, but I’m getting this error: avrdude: stk500_recv(): programmer is not responding. The board I Have selected is Arduino Uno and the Serial Port is /dev/tty.usbmodemfa131. I have tried switching serial ports and board type to make sure that I didn’t have the wrong ones selected. Pls Help.