Authorize.net : The underlying connection was closed

Question

I am working on a project where I am using Authorize.Net for payment processing.

It was working fine, but today I am continuously getting an error "The underlying connection was closed: An unexpected error occurred on a send." while calling any API function. Is this issue belong to authorize.net side?

I am working on test mode using sandbox account.

Answer 1

Add this line at the very beginning of your code

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12;