Whilst using the Google Adds app on an iPhone if you get the below message, we are working on a fix for this.
“before you can see billing in the app, use a computer to set up billing in your google ads account”
It means you cannot administer your billing or payments from your mobile phone using the app.
We are waiting for a solution for this. Visit back in a few days / weeks, however long it takes Google to resolve this matter.