TLDR: After scanning your passport photo page, you must scan the page showing your signature, which may be the same or the page above. Hold your phone horizontally 20-30 cm from the passport, aligning the screen box with the page. During scanning, a progress bar appears. After completion, review the photo and retake or submit it. Then, you'll be prompted to read the passport chip.
Scanning your passport signature page
After scanning your photo page, the next step involves scanning the page that shows your signature in your passport. This can be the same page as the photo page, or the page above. Please scan whichever page shows the signature, even if it is the passport page again.
To complete this, hold your phone horizontally to match the passport. Hold the phone 20-30 cm away from the passport, so that the box on the screen lines up with the photo page.
A progress bar will appear on the screen whilst the scan is in progress. After the scan is complete, you'll see the photo that has been taken on screen. You can submit or retake the photo if the wrong page is photographed.
You'll then be asked to read the chip in your passport. You can read more about completing that here.