With that being said, can you tell me a bit more about the dropdown menu you are using at checkout that doesn’t include Qatar? What part of the checkout process are you referring to? Do you see an error message of some sort?
Any screenshots and context you can provide will be helpful for this point.
In terms of the payment gateway error, we would need to look at your payment set up from your account. That is something our support team can assist you with. You can reach them at the following link.
As for Qatar not appearing in the list of countries - would you be able to send me your store URL so I can test this on my end, please?
After processing a test cart through your checkout, I’m not seeing a dropdown menu for countries on your payment page. I cannot replicate your screenshot. Are you still experiencing the issue? If you are, please specify which payment gateway you are using that is seeing the issue.