Just to add a little to the data point, I was asked at check in last month at OTP on a multi sector itinerary to HNL for my ESTA. My bags had been sent down the chute but the agent wouldn’t hand over my boarding passes until she’d seen the ESTA. Of course, as there was a queue behind me, I had trouble getting a connection on my phone and then connecting to the right page on the DHS/CBP website. Even as I stood aside, she wouldn’t serve other passengers until I’d eventually downloaded confirmation of my ESTA.

If you were in that queue, I apologise �� Lesson learned, I’ll have a PDF next time.