There is a special symbol in the Power library called Power Flag. KiCad’s ERC tries to help you to make sure that you actually have power pins powered (and don’t have two power sources connected). But, if you pass power through a passive part (or pull it from a generic connector) then KiCad doesn’t know where the power is coming from. The Power Flag symbol (looks like a diamond) is used to convince KiCad that there actually is a power source. It can be placed anywhere once on a power net (twice will cause other issues), but many of us advise placing it where the power logically enters your schematic as further documentation. See this FAQ entry:
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