The challenge is asking you to pass two arguments to the function.
But, what’s an argument? An argument is any value (string, object, number) you pass to a function. Depending on the function (and language), it may accept from 0 to any number of arguments. In this case, the function expects two arguments. To pass more than one argument, you separate them using commas.
The problem with your code
1 + 2 is not an argument, it’s an expression, and the result of that expression gets passed to the function as a single argument.
Basically, the sum is executed before it’s passed to the function, hence it counts a single argument.
So, with that definition, how many arguments are passed to a function call like this myFunction(1+2, 1+1+1+1)?