typescript chatAt funcation exist on type

I have a problem, there are 2 number values ​​on the route, for example localhost:8000/basket/00

I am trying to call number 2 on this route with the charat function, but there is a red line under the charat function and it gives me an error

const donationIndex = Number(route.params.id.charAt(0));
const detailIndex = Number(route.params.id.charAt(1));
const donation = ref(store.getters.currentSepet.donations[route.params.id.charAt(0)]);
const donationDetail = ref(
  store.getters.currentSepet.donations[route.params.id.charAt(0)].details[route.params.id.charAt(1)]
);