Amazon Pay / Payment not working for the UK

[cydesign]

Hi everyone,

Here is the error message once a sandbox customer has hit the 'amazon pay' button and then logged in: "The cart content has changed. Please, click on the button 'Pay with Amazon' and log in again.
When I hit the 'pay with amazon' button, I have to log in again.

No matter how often you do it, it always comes with the same error message and I can't figure out why.

Error comes up with the basic virtuemart template with all our various plugins disabled to ensure no compatibility issues.

Possible reason?:
I've read a post on a non-virtuemart site that Amazon pay requires the states (counties) field to be active, but I don't fully believe this.  We've tested with 'blank' county as well as some that we've added to VM.  When counties is activated, we can see the drop down when we use normal checkout. When we use Amazon pay, there is a dropdown at the bottom of the page, but it is blank.  I don't think counties really is the issue as counties is the most useless thing when it comes to shipping anyway.

I've spent hours trying to find a solution.

Joomla Version 3.8.2
Virtuemart: 3.2.6

There are 2 plugins (not sure why) for Amazon payments, I've tried it with just 1, then the other, then both activated.
AMAZON
Site   Plugin   3.2.1   March 31 2017   The VirtueMart Development Team   vmpayment       10015
      
AMAZON
Site   Plugin   3.2.1   March 31 2017   The VirtueMart Development Team   system       10016