Why can't I load an app onto my Kindle fire?

I keep getting the error message “There was an error purchasing xxx. Please click here to add an address to your account (this will open your browser) and try again.”
I have clicked the “click here” numerous times and have entered my email address and password at least 4 times and still get the same useless error message. I have an address registered. I can go online and look at it. This is extremely frustrating. What am I doing wrong?
Or, should I just admit this Kindle Fire is a stupid mistake and I should have gotten an iPad?