let [groupsToSend, setGroupsToSend] = useState([])

...

  const handleOnChangeGroup = (GrID) => {

      if (!groupsToSend.includes(GrID)){
        setGroupsToSend((prev)=>[...prev, GrID])
      } else {
        const index = groupsToSend.indexOf(GrID);

        if (index > -1) {
          setGroupsToSend((prev)=>[...prev].splice(index, 1))
        }
      }

    }