I am having a problem with my code to toggle a checkbox.

Also, just a note on brevity and clean code;

You shouldn't have to URL Encode the Record ID if the Record ID is a number.  URL Encoding will do cool things to special characters and spaces in strings, but it doesn't do anything to numbers.  

So, 

123 = 123  //true
URLEncode(123) = 123 //also true

Feel free to play with things here to see what it does if you're interested --> https://www.w3schools.com/tags/ref_urlencode.asp

~Rob