Trying to buy app - "Credit Card" greyed out

[pacman10]

I'm trying to buy an app (NavDroyd) for my HTC Desire but when I hit "Buy" it comes up with two buttons, "Credit Card" and "Cancel". "Credit card" is greyed out so all I can do is hit "Cancel" and go back round in the circle.

This is the first time I've tried to buy an app.

Can anyone tell me what to do next ? I've tried to help myself but a good hour going round the Android and Google troubleshooters and whatever else they are called has been unsuccessful.

 

[drowe]

I had that happen when I tried to buy an app from a foreign country and my credit card wouldn't allow it. Try adding a different credit card to google.

 

[pacman10]

I had that happen when I tried to buy an app from a foreign country and my credit card wouldn't allow it. Try adding a different credit card to google.

How do I add a credit card to Google ? I've been trying to find this out for at least 2 hours now. Any help appreciated.

 

[pacman10]

I had that happen when I tried to buy an app from a foreign country and my credit card wouldn't allow it. Try adding a different credit card to google.

I've found the cause and it is so silly it has me banging my head on the Desire's virtual keyboard.
In the selection box there is a very tiny circle next to "Credit Card" which, it turns out, I had to touch to turn it green and then it allowed me to select "Credit Card" as the means of payment. In my defence I must say firstly that since only one payment method (= Credit Card) was being offered (i.e. there was no choice) it didn't occur to me that I needed to take additional steps to select it and secondly that the little circle just looked like a bit of screen decoration.
The programmers need to make some changes here.