I see in the community that sometimes players are asked for the user id. Now I don´t know if it the same in all devices.
In my mobile I must log out and then click on the king symbol to see the user id. My suggestion are that the user id are placed inside the game so you can see it when your are logged in.
In my mobile I have a wheel up to the left. If I click on that I have a button "my profile". click on that and I come to my acount. It should be possible to put the user id in there. Much easier to find for user.