I am new at using Tmux. I have seen that it is quite difficult to copy-paste inside Tmux. So I searched for an easier method. Some sites suggested that I should use vim mode as I am quite familiar with vim. But, vim mode copy-paste isn't working. I don't know what I am doing wrong. But default copy-paste key binding working perfectly. Like Ctrl-Space is selecting text and Ctrl-w or Alt-w is copying the selected text inside Tmux. This is my ~/.tmux.conf file.

# Improve colors
set -g default-terminal 'screen-256color'

# Set scrollback buffer to 10000
set -g history-limit 10000

# Customize the status line
set -g status-fg  green
set -g status-bg  black

set -g mouse on

bind P paste-buffer
bind-key -T copy-mode-vi v send-keys -X begin-selection
bind-key -T copy-mode-vi r send-keys -X rectangle-toggle
bind-key -T copy-mode-vi y send-keys -X copy-pipe-and-cancel 'xclip -in -selection clipboard'

# remap prefix to Control + a
set -g prefix M-a
# bind 'C-a C-a' to type 'C-a'
bind M-a send-prefix
unbind C-b



# List of plugins
set -g @plugin 'tmux-plugins/tpm'
set -g @plugin 'tmux-plugins/tmux-sensible'

# Other examples:
# set -g @plugin 'github_username/plugin_name'
# set -g @plugin 'git@
# set -g @plugin 'git@

set -g @plugin 'jimeh/tmux-themepack'

set -g @themepack 'powerline/block/blue'

# Initialize TMUX plugin manager (keep this line at the very bottom of tmux.conf)
run -b '~/.tmux/plugins/tpm/tpm'

I am using Tmux 2.5. Thanks in advance for your help.