Thank you for reaching out to the Community! I’m happy to provide some assistance with locating a payment provider to ensure this gets resolved.
There are currently over 100 credit card payment providers you can choose from, allowing credit cards to be successfully processed on your Shopify store. I recommend checking out our Third-Party Payment Providers documentation for this list. For Greece specifically, it seems Revolut is not listed as a third-party payment provider nor listed within the Shopify App Store, but can choose from this list to select another supported payment gateway.
Please let me know if you have any other concerns!
Yes, it is now available via Stripe and the third party checkout solution Easy⥔Pie Shopify Stripe Checkout, that supports most payment methods supported by your Stripe account.