It might be worthwhile stating any information about what you are doing. Are batteries in the senders? Have the senders been switched on? Does their channel match the receiver channels? Has the receiver been switched on?
At any rate, the specification for the line output is one mixed output, balanced or imbalanced. That will be a mono output. The usual connection to a PA worth its name is using a balanced cable with 6.3mm TRS plugs on both ends. It's kind of unusual for a PA to have RCA inputs, and a TRS to 2×RCA cable is the wrong cable anyway. You could use a mono TS to single RCA cable, but a balanced cable will have quite better signal quality, assuming that your PA actually has a balanced input.