DJM A9 with DJS 1000 and RMX 1000 Connectivity Send & Return

Hello Community, I am really a newbie within DJ. I From my ordered Products only the DJM A9, DJS 1000 and the RMX 1000 arrived, the 2 CDJ 3000 are still postboned to August 2025. So now I try to learn with things I have. I connected the hardware with Send & Return from A9 -> DJS 1000 -> RMX 1000 back to A9 Return. By using only this connection, I will not get any signal to my A9 and I dont know why! When connecting an additional chinch cable from DJS 1000 to A9 e.g. Line in Nr. 4, the DJS 1000 signal comes in and output to amp works fine, but I cannot use the RMX 1000, means no effects. I checked send and return very often, the RMX shows incoming signal, DJS as well, means the routing should be fine. Can someone please help me to solve my connectivity issue? would be nice :-)