How to use tmux copy / paste in Termux? I installed Termux and using the pkg system installed tmux.  

However, the tmux that installs doesn't appear to support copying and pasting.  I can enter copy mode, but I can't select text and copy it to the clipboard using the spacebar and the enter key.  Is there any way to go about this?
Try having this line in your ~/.tmux.conf file:

set-window-option -g mode-keys vi


This enables a set of vi key bindings that seems to work fine. I used the Spacebar and Enter keys to copy that line from within a tmux session running in Termux and pasted it into this textbox in Chrome with Ctrl+v.