Connecting FS-148F-POE to FortiGate 70G, very simple network

I'm working with a very simple network, comprised of a Fortinet Switch, Router, and some endpoints.

The Fortinet switch is a FS-148F-POE (48-port), and the router is a FortiGate 70G.  Both were purchased recently through BlueAlley via Amazon.

The router is on firmware v7.4.11 build2878 (Mature).

Initially, the switch was connected to the router through the router's port #5, a FortiLink port was not used.

Everything was working fine but I thought it better to connect the switch to the router via a FortiLink port.  So I moved the cable connecting the switch from the router's Port #5 to Port A.

At this point, the router recognized the switch and I was able to Authorize and Register the switch.  I was also able to upgrade the switch to the suggested latest firmware (v7.6.6 build1137).

But after the firmware upgrade, the switch rebooted and then vanished under "Managed FortiSwitches," though it still appeared under System/Firmware & Registration.

And at this point, none of the devices attached to the switch (a handful of PCs, VOIP phones, printers, etc.) that had worked fine previously, seem to be getting any DHCP action from the router.

I'm not sure if I missed a step or if this is a matter of licensing or what.

This is my first time dealing with Fortinet stuff so don't assume I know anything.

I was just attempting to get the Fortilink connection going and continue to use the vlan 1 for all my devices, as I had before.

What did I do wrong?

Any and all help is appreciated.