unity on trigger enter not working code example

Example 1: unity on trigger enter

//for unity c#

private void OnTriggerEnter(Collider other)
{
    // code
}

Example 2: void ontriggerenter not working

2D for 2D (OnTriggerEnter2D) and 3D for 3D (OnTriggerEnter)
at least one object needs to have rigibody, and collider set to isTrigger

yea and this is for unity game engine only

Example 3: void on trigger enter unity

void OnTriggerEnter(Collider other){}