GL-SF1200-c52 no ethernet, WAN working

Hello all,

I bought a new GL-SF1200-c52 and connected three PCs.
The GL-SF1200-c52 is connected to a Fritzbox, which is providing the internet connection.
I can access the subnet of the fritzbox and I can access the internet. But I can´t acces the other PCs which are connected with the switch of the GL-SF1200-c52. (The GL-SF1200-c52 replaces an older router, so it should not be an issue of the clients, because with the old router it´s working)

I checked all settings like VLAN and turned off the VLANS, but still not working.
Does anybody has an idea?

That's not a supported device here, ask gl-inet.