The app will automatically take a photo of your ID. If it doesn't, it could be because of the following reasons:
Your photo is not within the green box.
The instructions are not being followed. For example, the app might be asking you to "show only one face". This means to zoom in your ID so that it shows only one of the photos/ faces on the ID. It does not mean to take a selfie.
The picture is taken on a low light environment. Move to a better lit environment.
There are multiple foreign objects in the background. Take the photo against a plain background, like a desk or a wall.
The camera is too far from the photo ID. Move the phone camera closer to the photo ID that it can clearly distinguish the photo on the ID
The camera is too close to the photo ID. Move the phone camera slightly farther ensuring that the photo ID details and the "face" on the ID itself is clear.
It should then take a photo of the ID.
If there is an issue with the ID you submitted, the app may show the screen below. In this case, make sure to make a second attempt at taking a photo of your ID.
If the issue persists, try again but this time, make sure to take a screen recording before you try again. This way, you can forward us the video which will help us diagnose the issue faster.