As standard best practice, which configuration should be performed before configuring FortiAPs using a FortiGate...

Setting the wireless controller country setting is a standard best practice that should be performed before configuring FortiAPs using a FortiGate wireless controller. The country setting determines the regulatory domain and the allowed channels and power levels for the wireless network. The country setting must match the physical location of the FortiAPs to comply with local regulations and avoid interference issues. References: Secure Wireless LAN Course Description, page 5; FortiOS 6.4.0 Handbook - Wireless Controller, page 24.