kindle-notebooks user agent workaround

It looks like there is a workaround for viewing Scribe notebooks with a web browser:

• Login to amazon.com
• Using browser developer tools, change the user agent string to a mobile device, such as "Mozilla/5.0 (Linux; Android 12; SM-X906C Build/QP1A.190711.020; wv) AppleWebKit/537.36 (KHTML, like Gecko) Version/4.0 Chrome/80.0.3987.119 Mobile Safari/537.36"
• Paste this URL: https://read.amazon.com/kindle-noteb...o_mm_yn_na_kfa

Safari is able to view thumbnails and navigate into folders, but cannot view notebooks (but this was broken before Amazon closed the 'front door').

However it all works on Microsoft Edge, presumably Chrome and FireFox too.

I do not understand the function/meaning of the ref_ query parameter. I copied the URL from the description of this YouTube video: https://youtu.be/GT5TbOf3k1M?si=UGhjXq68QAQLJ_Ob&t=842

Things don't seem to work without it. I wonder how it was discovered?