ETA app issues

If I remember correctly from when I did mine in December, the instructions on which part of the passport to photograph are unclear at best and misleading at worst. If you're trying to photograph both the ID page and the page opposite (ie both pages of the open book), try doing just the ID page (just the single page), or vice/versa.

I had some challenges with the photo page, I think because of the glare on the page from the overhead light. Try moving to another location, and as noted in prior reply, they want just the photo page. If you still cannot get the app to work, you can apply online. Just make sure to use the official website and not a commercial one.

https://apply-for-an-eta.homeoffice.gov.uk/apply/electronic-travel-authorisation/how-to-apply

This forum thread at about 12/27/2024 has discussions similar to your problem: https://community.ricksteves.com/travel-forum/england/uk-eta-application-experience
With the app, you scan the back cover. With the website, you photograph the information page. We used the website and had to take/submit a photograph multiple times before it was accepted.

I found it quick, but I did have to edit the photo of the passport photo page to crop extraneous detail and just show the page itself.

Use the website

As I posted in the other ETA thread here, the same thing happened to my mother when applying. I had no issues. After a week of trying it became clear that it was never going to let her apply via the app, for whatever reason. So we did it by using the option to apply on the web. This meant taking and uploading the passport info page photo and selfie photo. It took quite a few tries to get the selfie photo to meet their specifications. But I'd say this is your best option.