Responsys block with list directive breaks browser view

Question

Data is coming in through an API and the payload contains items as a field with multiple properties such as Name, Quantity, Size, color.

Here is the email block that uses the List directive:

Name: ${ship_firstname} <br/>
<#assign itemspayload = items?eval> 
<#list itemspayload.items as item>
    <#assign PName = item.ItemName>
        Product: ${PName} <br/>
        <a href="${form(campaign.name, 'ship_firstname','PName')}"
            style="color:#5F5F69 !important;font-family: Gilroy-Bold, Arial, sans-serif; font-size:14px;font-weight: 600; text-decoration: underline !important;" class="fnt11">View in Browser</a><br/><br/>
</#list>

The view in browser link just displays a blank page. Can anyone point out to the right way of implementing this?

I have tried assigning the value to a variable and passing that in the view in browser link.