Hi Sascha.
Welcome to the forums.
Edit: make sure the interface on the fgt that has the 210B is connected to, has capwap enabled.
The 210B has to be able to to discover the wireless controller (i.e. 60D) on it' s own, using 4 possible methods, which are listed in the Advanced WiFi controller discovery section of the
Deploying Wireless Networks.
First off, I would check the firmware patch notes for both the 60D and 210B to make sure both are compatible with each other. After that, choose one of the methods for wireless controller discovery. I prefer the DHCP-method, but if you are using static settings then you will need to configure the Wireless Controller IP address into the 210B.
You should be good to go after that. If not, I suggest connecting a serial/console cable to the 210B and reboot the AP and watch the boot process for any unusual error messages via putty or other serial/terminal software.
NSE4/FMG-VM64/FortiAnalyzer-VM/6.0 (FWF30E/FW92D/FGT200D/FGT101E/FGT81E)/ FAP220B/221C