The Gateway Server entries in the Acronis Files Advanced Web admin tell the system which Gateway Servers the mobile apps will communicate with to retrieve files. Normally there's a default entry and that should be all you need for a trial (more can be added for scaling purposes later if needed). If that's not present due to an earlier problem or configuration change, you can add it as follows.
1. Navigate to Mobile Access --> Gateway Servers
2. Click the button Add Gateway Server.
3. Pick a Display Name. This may be visible to users in the mobile app, depending on other settings.
4. For Address for Administration set the local IP address of the server. Do not use the public IP address or DNS name. Note that you must append the port number if not using the default port of 443. You can check through the Acronis Configuration Utility that's installed on the Windows server. If the Gateway Server tab of the utility shows a port other than 443, append it to the Address for Administration (e.g., 172.16.2.15:444).
5. Select "Use alternate address for client connections".
6. In Address for Client Connections, set the DNS name for the server, if you have one (e.g., mobile.mycompany.com). If you don't have one yet, you can start with the private IP address of the server. If you appended a port number in step 4, then do the same here (e.g., mobile.mycompany.com:444).
7. Get the Administration Key using a browser running on the server itself. You may be able to browse to https://localhost/gateway_admin to see it. If the Gateway Service is not using port 443, then append it (https://localhost:444/gateway_admin). If that doesn't work, use the private IP address of the server, appending the port if it's not 443. Remember to browse using https:// not http. For security reasons, the Administration Key will only be displayed if browsing from the local server.
8. Enter the Administration Key.