i have tested amasty onestep checkout with magento 2.4.3-p1 using luma sample data.
amasty onestep checkout didnot throw error if input "Invalid City State Postal Code" when payment method is paypal.
it redirects to shopping cart page directly without error alert. it would make customer confused.
paypal will throw an error if we input "Invalid City State Postal Code".
please refer
https://www.paypal.com/webapps/mpp/shipping-address-outside
i have to disable paypal validation by changing core code.