document.getElementByID is not a function

This error usually occurs when you try to use the `getElementById` method on a variable that is not a valid DOM element or when the method is misspelled. Please make sure that you have spelled the method correctly and that the variable you are trying to access actually exists and is a valid DOM element. Also, check if you are accessing the element before it has been loaded into the DOM. One way to ensure that the element is loaded is to wrap your JavaScript code in a `DOMContentLoaded` event listener. For example:

document.addEventListener('DOMContentLoaded', function() {
   // Your code here
   var myElement = document.getElementById('myElement');
   // ...
});