NewsBlur does not recognise seemingly valid RSS

problem
#1

I’ve an order at Customer Login - Niton999, which I should be able to subscribe to using https://www.niton999.co.uk/rss/feed/index/type/order_status/?data=eyJvcmRlcl9pZCI6IjEwMTM3NiIsImluY3JlbWVudF9pZCI6IjEwMDAxMTExNjAiLCJjdXN0b21lcl9pZCI6IjI2NDAzIn0%3D&signature=22f78264c53c82069fd2bf8ea20ae81e0b81df1c21b2d06ca40d07c40bfeda5d.

In case that key becomes invalid, view-source:https://www.niton999.co.uk/rss/feed/index/type/order_status/?data=eyJvcmRlcl9pZCI6IjEwMTM3NiIsImluY3JlbWVudF9pZCI6IjEwMDAxMTExNjAiLCJjdXN0b21lcl9pZCI6IjI2NDAzIn0%3D&signature=22f78264c53c82069fd2bf8ea20ae81e0b81df1c21b2d06ca40d07c40bfeda5d displays:

<?xml version="1.0" encoding="UTF-8"?>
<rss version="2.0" xmlns:slash="http://purl.org/rss/1.0/modules/slash/">
  <channel>
    <title>Order # 1000111160 Notification(s)</title>
    <description>Order # 1000111160 Notification(s)</description>
    <generator>Laminas_Feed_Writer 2 (https://getlaminas.org)</generator>
    <link>https://www.niton999.co.uk/sales/order/view/order_id/101376/</link>
    <item>
      <title>Order #1000111160 created at 20/04/2024</title>
      <description><![CDATA[<p>Current Status: Processing-FS Acknowledged<br/>Total: <span class="price">£50.95</span><br/></p>]]></description>
      <link>https://www.niton999.co.uk/sales/order/view/order_id/101376/</link>
      <guid>https://www.niton999.co.uk/sales/order/view/order_id/101376/</guid>
      <slash:comments>0</slash:comments>
    </item>
  </channel>
</rss>

It certainly appears to be valid RSS (I know, that’s potentially a misnomer, considering how unstandardized it is in comparison to its Atom successor) yet NewsBlur doesn’t accept it:

image

This address does not point to an RSS feed or a website with an RSS feed.