A few suggestions:
First check the settings for the input field. I set mine to take numbers. If you’re allowing text, and entering a dollar sign or a comma, you’ll have this problem.
Second, look at the code. Do you see any red squiggly lines under anything? If so, hover your cursor over that part of the code, and you’ll be given an explanation of what’s wrong.
Third, stick some console.log statements into the code to see where things are going wrong. The first place I’d put one is immediately under the const salesPrice assignment. Log the value of salesPrice and see if it’s a number.