For initial tests, it is recommended to have the server computer and Android devices connected to the same local area network. In the simplest case, they should be connected to the same Wi-Fi router.
Server computer should be connected to the network over the cable, but not over Wi-Fi. Wi-Fi connection is good for temporal testing, but not for permanent usage.
Server computer must have fixed IP or DHCP reservation on the router to eliminate IP address change.
Fixed WAN IP address must be acquired from the internet provider. This IP address will be used to connect WalkieFleet client over the Internet. Dynamic WAN IP is ok for tests, but in real operation, unexpected IP change on the router will prevent all clients from connection.
Apply NAT port forwarding on the router between router WAN IP address and server LAN IP address. Information about ports to be forwarded can be found in WalkieFleet Server Manager (Initial Server Configuration, WalkieFleet Network Settings).
Make sure the ports required for WalkieFleet operation are not blocked by Antivirus. In case when client can't connect to the server, temporally disable Antivirus software to check if it prevents WalkieFleet operation.
Besides Antivirus and firewall software, ports can be blocked by networking equipment. Simple Wi-Fi routers usually have firewall disabled by default, but in more complex corporate networks such security settings can be applied by IT department.