If your Fortigate doesn't support version 5.6.1 or later, you can't manage it with a managed IP address. But you can use Fortinet Cloud to manage them.
MikroTik RBcAPGi-5acD2nD-US: High-performance Dual-Band 802.11ac Access Point
35 Review
Wi-Fi signal amplifier (repeater) TP-LINK TL-WA860RE, white
21 Review
Ubiquiti NanoStation locoM2 2.4GHz airMax 8dBi CPE - Indoor/Outdoor High Performance Wireless Device
30 Review
Wi-Fi router Keenetic Hero 4G KN-2310, white
76 Review
HB-UMLS Sabrent USB 2.0 Hub with 4 Ports and LED Power Switches for Each Port
12 Review
π StarTech.com NETRS232 Serial to IP Ethernet Device Server - DIN Rail Mountable - Serial Device Server - Serial Over IP Device Server (Black)
4 Review
π uni USB C Hub with Ethernet Adapter, 4K HDMI, Gigabit Ethernet, and 3 USB 3.0 Ports for MacBook Pro, iPad Pro, XPS
11 Review
UGREEN USB 3.0 Ethernet Adapter Hub with RJ45: Fast Gigabit Ethernet Converter, 3 Ports USB 3.0 Hub Compatible for MacBook, iMac, Surface Pro, Chromebook, Laptop, PC
11 Review