I am using PayPalStandard plugin of NopCommerce. When I placed the order & make payment with paypalstandard plugin after successful payment on paypal, it redirects to mercha
The answer that worked for us was listed on the PayPal blog post, Upcoming Security Changes Notice. There are a number of things listed in the post, but the one thing which we did, and that worked, was PayPal SDK Updates. We updated using NuGet and everything started working again.