FNB Banking App Login Issue

FNB,I am currently struggling to login on the app.I have the login details but every time I type in my username it doesn't allow me to proceed to use the app instead it will tell to re-enter my username and I have been doing this for the millionth time and it's still not working but on my laptop I can login.I want to use the app to a create a virtual card and to verify my browser.Can you please kindly assist me with this problem.