Here is another photo. Back of the leaves...

How many leaves are affected? All or a few?

What conditions of light, temperature & humidity?

Hi Jean,

All leaves or at least most leaves are affected.
The plant faces a south-east window, and gets sun from 7-11 am.
Temp. variation 16-20 C/ 61-68 F
Humidity - 45-55%

I spray the plant with water twice a day.
The plant was twice infected by spider mites.
I don't remember exactly when the spots and the leaf curling started. Possibly by the end of summer.
Each time I sprayed it with Neem oil / horticultural oil mix. The 2nd time, I was a bit more drastic. I took it outside in -12 C/ 10.5 F and sprayed it. All the leaves died. But when the sprouted they still had the spots/ curling.

Thanks again...

It's a bit challenging to see detail n the underside of the leaves.

But my first impression was that it was likely edema. I still think so because of your moderate temperatures, relatively high humidity, & water sprays (seldom ever need that in spite of what you read). If so, not a problem.

That said, I do see one small aphid on the leaf toward the left. Squish it and remain alert for more of its kin.

Hi Jean,
I took a couple of more pictures. Hope they are better. The first one is the back of the leaf.
I assume you're right, it seems I over watered. I'll wait until it dries out.
Thanks for the tip on the aphid. I'll take care of it.

Front of leaves...