Hi, I think I posted something like this before, but I fully understand the frustration in using the trampolines. Happened to me the first few times.
You have 4 trampolines, and some fleet that you want to move.
Put 2 trampolines and the fleet you want to move on COORDINATES "A". Put 2 trampolines on COORDINATES "B"... the destination.
Once the trampolines and the fleet are on the respective COORDINATES (not planet, not moon)... select the fleet you want to move from "A" to "B". Select the destination coordinates "B" (where receiving trampolines are) and choose mission ACS D.
At the bottom, next to the "Send" button, you will have "Send thru trampoline" button... use this.
And you should be good to go :D
Happy trampolining!