Please not that it is not possible to establish a connection whilst being connected to the WiFi network of OTH (this includes both “Eduroam” as well as “secure.hs-regensburg.de”) as you then already are connected to the university network. Thus a VPN connnection is not necessary anyway.
If you encounter connection issues, please check the following.
Do you have a sufficiently fast internet connection? Using mobile data 3G should be available; slower connections like EDGE could potentially be too slow.
Are the configuration parameters correct? Please check with a click on “Settings” within the FortiClient app whether server and username are correct
Are there updates for the FortiClient app available? In case the most recent version of the FortiClient app is not installed, there could potentially be compatability issues with the VPN-Gateway.
Restart your smartphone