Hello,
Under normal circumstances WooCommerce shows this string when there are no payment gateways configured AND the customer has not set their billing country: https://github.com/woocommerce/woocommerce/blob/3.7.1/templates/checkout/payment.php#L33
It seems that Multi Currency Premium somehow causes this plugin to not be available.
I can’t know right now why this plugin is incompatible, because I don’t have its premium version. Can you live without it?
Additionally, you mentioned that you don’t collect customer information such as the billing country. This shouldn’t be a problem as long as the payment gateway is available. You will also not need any shipping info if you set your products to be virtual.
with regards