If you are using Payflow Pro Hosted and you have made sure that the settings below are all correct in Paypal Manager, but you are seeing the error, "Merchant Design Identification Error", when trying to checkout from your Pressero site, then please try resetting the selected layout for the hosted page.
Transaction Process Mode: Live
Enable PayPal Credit: No
Payment Confirmation > Show Confirmation Page > On My Website
Enable Secure Token: Yes
Customize Your Page: Layout C
This error indicates that your payment method is successfully connecting to your Paypal account, but there is some kind of an error happening when showing the hosted page design layout.
To reset the layout, go to the Customize Your Page area in Paypal Manager, set it to use a different layout -- Layout A or Layout B -- then Save and Publish. Then go back to the Customize Your Page area, select Layout C, and Save and Publish.
Try checking out on an order again after resetting the layout, and please open a ticket to Aleyant Support at support.aleyant.com
if you are still seeing a problem after resetting the layout.