Hi all!
My name is John and I'm a Guru here at Shopify!
As stated earlier in this thread; it would be necessary to prove your United States citizenship in order to apply to use Shopify Payments there.
If you are not a US citizen you can still apply to use any of the other gateways available in the USA to take payments in your store.
Some of these gateways will be direct, meaning they are fully integrated to your Shopify checkout and customers do not navigate away from Shopify when paying.
Others will be indirect, or external; meaning the payment gateway opens in a new window where the customer makes their payment.
You can see a partial list of direct vs external gateways here though to be completely certain of how a given gateway works you would need to reach out to the specific company running that gateway. :)
Best of luck with everything here!
Regards,
John