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You just got the wrong circuit from Google.

That is not a true summer circuit where all the input voltages are added together.

For that you need to use a resistor in series with each the sources to the (-) input with an equal value resistor from the output to that input (try 10kΩ for all).

Connect the (+) input to ground.

That will invert the signal, so if you want non-inverted, you need to add another inverting op amp at the output of the first.