The picture of your setup isn’t the same as shown in the diagram.
The output of this kit doesn’t produce a voltage. it only opens and closes a wire. just like a regular switch in your house.
You’ll have a wire from your power supply running to the motor. Then the other wire coming from the motor you connect to the NO or NC contact (depends on your application) of the kit and then another wire coming from the kit (COM) goes to the power supply. As shown in the diagram.
Sorry I formatted that strangely, I had meant that I had tried the diagram in a separate attempt with no luck. (https://i.imgur.com/ezVqP1d.jpg)
Also I’m not sure if this matters or not but what you said and what the diagram shows is slightly different. The diagram shows that you connect the motors 2nd wire running to the COM and a wire from the NO/NC contact over to the power supply.
Let say the positive from the battery is going to the light bulb and the negative is going to COM (Common) the Negative from the light bulb is connected to NO (Normally Open) when the relay is engaged the light bulb will turn on.
The other positive and negative from the battery to the other side of the board are just to power the circuit. see below.