How to set up on mobile phone

I’m not very technical but have set up OnlyKey on my laptop - works well but cannot seem to set it up on my mobile phone.
There was a different URL so I set up a new slot for my email on mobile phone using mobile URL.
It got to the URL. I tapped on screen in Username box but nothing happened. Also tried Tab and Return but still would not enter my user name.
Any halp would be appreciated.