I watched the video, but I don't use Home Assistant.
And that doesn't solve the problem.
In any case if I put 1.5 volts on the analog input, in the Monitor part of the KC868_A16 card, I should see 1.5V and not 2.01Volts.
ADC is in the A16 card in any case the displayed value must be correct.
Whatever the system that will read the value, it must be correct at the source therefore KC868_A16.
Yes the gnd is connected
Look at the photos of the posts
I test the capacities, reliability, etc of the card before buying others.
There I am on the analog inputs and I look at the reliability of the measurement, I send 1.5v I see that I have 2.01 volts so problem