Can't Add My S2 Motion Sensor ZSE18 to Home Assistant

Exclusion is just a soft Z-Wave reset. A device doesn't need to be included first to be able to excluded. Here's how to do it:

In Home Assistant: open Settings > Devices and Services > Z-Wave JS > Configure
Click on Remove Device
Click on Start Exclusion
Press the Z-Wave button 3 times very quickly to finalize the exclusion process
The device will now be removed, but that won’t show until you restart Home Assistant
Run a Heal Network so all the other nodes learn about its removal

After exclusion is confirmed, try adding the Motion Sensor back to Home Assistant again.

If that didn't work, here are some troubleshoots we find helpful:

Try the exclusion process again! It's possible the exclusion commands from the first run weren't registered correctly.
Try the exclusion process again, only this time instead of pressing the Z-Wave button 3 times quickly, press it 4-5 times as quickly as possible. This can help make sure the commands go through.
If your sensor is in a location that is far away from the hub then it may be having trouble communicating. Try bringing device closer to the hub to see if it connects in a closer location. If it connects without issue in the new spot, then the first location may be out of range or there may be too many interferences in that area.
Alternatively, you can try adding a Z-Wave signal repeater (or any non-battery powered Z-Wave device) between the sensor and hub to see if it resolves the issue. A Z-stick or hand-held secondary controller can then be used to add the sensor to the network.
Whenever moving the sensor to a new spot, we recommend excluding and re-including the device anew so that the hub can find the most efficient communication route to the device every time it's moved.
And if you find that your sensor is connected but it's not responded to remote commands, check out these tips for troubleshooting connectivity.

If you've tried all the above with no luck, let us know! Our team is ready to help.