Zip tie is there to make the installation processes easier.
|Remove belt clip after installing the seat belt in the vehicle.|
If you cut the zip tie prior to installing it, the seat belt will retract all the way in. To release the seat belt, it needs to be in the same position as it is in the vehicle. You can also mount seat belt assembly main unit in the vehicle and then pull on the seat belt and it will release. Here is a video that can help you with this as well.