Is your Battery (probably the trailer's "House Battery") fully charged?
If you can find the Motor that powers your Slide Pump, if it only has two wires, the two relays must BOTH be good for the slides to work in both directions. We think of the "OUT" relay as going "on" to go Out, and yes it must, but the "IN" relay also has contacts that have to make up in its "off" position. Likewise, to go back "IN" that relay has to make up as "on", but the "OUT" relay must have its "back" (or "normally closed) contacts made up in the "off" position.
What's happening is the two relays work together to reverse power polarity on those two motor wires.