The web-api requires that the file be accessible for the server. So yes, you need an application server on the machine running service pages. Is there a reason you can't install a local server? I know that it is sometimes not possbile, but in most cases this is the simplest solustion.
Our users are accessing servicepages through internet. In order to secure our environment, we have splitted the service pages and application server on two different machine and there is a firewall between servicepages and application server.
In that case, you have no choice but find a way to transfer the attached file to a temporary location on the application server. Probably copying it with ssh or https will be safe and simple enough to work via the firewall.
In this case I have to FTP/SSH the files from some directory in service pages server to some directory in application server either manually or scheduled manner then attach those files with the specific service calls manually.
Is there anyway how can automatically link the files to the specific call ID once the files reaches to application server from service pages.