Hello,
I’m really stupid and forgot how to rotate a vector. I know it has to do with the fact that degree system works from -180 to +180. But how can I rotate a vector in this system 180 degrees? I want to invert the direction basically. I knew how to do it once, but I forgot. 
Multiply it with -1
to invert you multiply by -1.
There are also rotate vector around axis nodes. Just watch because some are for radians some are for degrees.
If I multiply it by -1 nothing changes, the resulting direction is still exactly the same as without -1 multiplication. o_O
Here is my exact problem. I have a wind vector that has a certain direction. Then I have a flag blueprint which checks said wind vector and needs to set it’s own rotation the same as the wind vector’s direction. Which all works fine. The only problem is that my flag mesh is pointing backwards instead of forwards and therefor I have to rotate said flag mesh 180 degrees or add 180 degrees to the wind direction so that it rotates properly.
Multiply VECTOR by -1, or add 180 to rotation (do not worry unreal mostly does this correctly).
Ps.
Take screenshot of graph that calculates rotation of flag, and post it here, you may be doing some silly mistake there.
Here is the normal rotation, which works as intended. Now I only need to add 180 degrees so the flag is flipped.
Multiply “Wind Direction” by -1 (Vector * Int or Float) and connect it to the “In Vec” in RotationFromXVector.