Try to apply the moment on one point/node. Use RBE2 or RBE3 to connect this node to the desired surface.
and check if your boundary conditions at the other end is valid (all fixed for example)
3D solid element formulations only define translational stiffness at connected nodes, so you cannot apply a moment load to a node that is connected to only solid elements.
The suggestion is to create a point (or node) at the location where the neutral axis intersects the face that you want to apply a moment load on. Create a Point to Face (or a node to node) 1D connection from this point (or node) to the face (or all of the nodes on the face). Specify that the connection element type be RBE2 or RBE3.
Note that the instructions within parenthesis above are for an FE only model with no underlying geometry available.