which gnd did you define as power out? I hope not the one of U1!
Place a power flag near on the gound net near where you connect ground to your external power source. (Most likely a connector)
Do it this way to ensure that ERC can detect if you have connected the ground pins of your symbol to where you get power into the PCB
@Gozzle: I hope you not ignoring my response. I were telling you to add PWR_FLAG for the GND. And should not try to use Power Output type for any symbol as much as you can.
It is in the same library as the GND symbol but it is for a very different purpose.
The PWR_FLAG symbol has a single pin defined as power output. It is intended to mark the place where you supply power. (The connector where you connect to your external power supply, after a passive device in the supply line like a fuse, …)
The GND symbol has a single hidden power input pin. Such a pin is a global label (yes this is hacky). Such a symbol is called a power port or power symbol.
I don’t like the way they use it in this tutorial. By connecting the power flag directly to a power symbol you loose the reason to have it. I would suggest to place the pwr_flag symbol as near as possible to the place where the board is supplied.