Mouse – How do I activate the forward and backward buttons on Remmina?

I'm using Remmina to remotely connect Ubuntu to my EC2 bare metal machine. I'm trying to use the back and forth buttons on my mouse, but they do not seem to work. xev registers the event on my local computer (Ubuntu), but not on the remote computer. I've upgraded to the latest Remmina (SPICED) version for this to work, but I'm not sure if I'm configuring it properly. Can somebody help me with it? Many Thanks!