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Get Paypal Express working with OneStepCheckout and Magento 2
As of OneStepCheckout 1.2.044 you can control some aspects of additional validation for your store REST endpoints. This includes 2 types of access control for verifying AJAX requests and control access to REST endpoints via Google's invisible reCAPTCHA v3. Most commonly used against carding attacks that plague Magento 2 based stores or other attacks against your site REST endpoints.
If you are using the official Stripe Payments extension from Stripe, you can experience some rendering and layout issues depending on your Magento configuration.