How to Fix CORS issue on WebToLead

I'm having an issue with the following code. The status of the request is 200 however it doesn't actually send anything because of a CORS issue. I'm aware that I need to add the host URL through the Salesforce platform but is there anything else I need to do since the engineers I've spoken to mentioned that the template code I used to build this form was correct. 

{⌗ Start of Salesforce Form ⌗}
<form class="with-us-form" action="https://webto.salesforce.com/servlet/servlet.WebToLead?encoding=UTF-8" method="POST">
<input type=hidden name="oid" value="00D9P000003QZ7w">
<input type="hidden" name="debug" value=1>
<div class="container">
<div class="row">
<div class="col-6">
<div class="row">
<div class="col-6">
<input class="form-control line" type="text" name="first_name" placeholder="First Name*"
required>
</div>
<div class="col-6">
<input class="form-control line" type="text" name="last_name" placeholder="Last Name">
</div>
</div>
</div>
</div>
</div>
</form>