I’m not sure if it’s the right category to ask this, but…
I’ve got an old smartphone. I purchased it back in 2009, but the model dates to 2008. It’s NOKIA E63.
But the mobile browser that I use in it is rather new. It’s Opera Mini from 2012, I think. (ver. 7.1.32444)
And I get a cert error when I try to access my site. Before I installed Let’s Encrypt, I’d been using a “regular” cert and I hadn’t got any errors.