Running a dotnet 8.0.202 in linux (Rocky OS) with Nginx webserver. We have proxied the internal dotnet service running at localhost:5000 to https://example.com and everything seems to be working fine.

We are using letsencrypt with Nginx for SSL.

When we are calling paypal URL for payment process at https://api-m.sandbox.paypal.com/ application throws error by saying

System.Net.Http.HttpRequestException: The SSL connection could not be established, see inner exception.
 ---> System.Security.Authentication.AuthenticationException: The remote certificate is invalid according to the validation procedure. 

I have tried to implement this, but didn’t worked:

bool RemoteCertificateValidationCallback(object sender, X509Certificate certificate, X509Chain chain, SslPolicyErrors sslPolicyErrors)
  {
      // Always return true to bypass SSL certificate validation
      sslPolicyErrors = SslPolicyErrors.None;
      return true;
  }
 
  // Set the certificate validation callback before making the API call
  ServicePointManager.ServerCertificateValidationCallback += new RemoteCertificateValidationCallback(RemoteCertificateValidationCallback);

Can someone please give me some more debugging tips?

Many thanks in advance.