Send 'Comment' or additional field with Global Payments HPP - PHP SDK - RXP JS

Question

How do you send additional data through to Global Payments like 'Comment', 'CustomerNumber' or 'ProductId' using the HPP with PHP SDK / RXP JS?

I have tried the following and cannot see any documentation for it.

// Add 3D Secure 2 Mandatory and Recommended Fields  
$hostedPaymentData = new HostedPaymentData();  
$hostedPaymentData->customerName = 'Your name';  
$hostedPaymentData->customerEmail = 'email@email.com';  
  
// not working  
$hostedPaymentData->customerNumber = '48898984';   
$hostedPaymentData->productId = '48898984';   
$hostedPaymentData->comment1 = '48898984';