jQuery in WordPress. Uncaught TypeError: undefined is not a function

Trying to load a calculator widget for interest rates.

Unfortunately I’m getting an Uncaught type error, with this script:

$('.hire-purchase.calculator-widget').each(function() { 
 var app = new LHV.HirePurchase(); 
 app.init($(this)); 
 });

It is working fine, when I load the widget in a separate .html file with all the necessary script and jQuery. Although when I add it to the webpage in development it conflicts. What could be the problem?