So...I have been doing dry runs for purchasing Eiffel Tower tickets and I have not been having success. Specifically, I get the tickets into my cart, then select "validate" and--POOF--the cart goes empty. Although I have time yet--our trip isn't until early April--I finally decided to get help from the ET website. They advised switching to a different browser and it WORKED! Of course, I didn't actually finalize the purchase of the tickets, since the dates I want aren't yet available, but, hey, at least they stayed in my cart! Here's hoping I don't find a new difficulty when finalizing the actual purchase in early February.
BTW, Google Chrome is my everyday browser, but it took switching to Microsoft Edge to make the ticket purchase process (seem) to work.
Merry Christmas and Happy New Year to y'all!