Linux – how to paste into tmux from system clipboard

I'm using tmux with WSL (Ubuntu 18.04) and I can't figure out how to paste into tmux. Pasting works great with the normal terminal by simply right clicking, but this doesn't work in tmux.

All the tutorials online seem to explain how to copy text from tmux to system clipboard which I have working through tmux-yank, but no luck for system clipboard to tmux.

Edit: it seems like this works for most people by default. What information can I provide that would be most helpful to debug?

Update: I realized that right-click currently lets me move the bar that separates my two vertical tabs. I didn't set this behavior anywhere, where could this be coming from? Here is my tmux conf which I got online:

# Set a new prefix / leader key.
set -g prefix M-j
bind M-j send-prefix

# Allow opening multiple terminals to view the same session at different sizes.
setw -g aggressive-resize on

# Remove delay when switching between Vim modes.
set -sg escape-time 10

# Allow Vim's FocusGained to work when your terminal gains focus.
#   Requires Vim plugin: https://github.com/tmux-plugins/vim-tmux-focus-events
set -g focus-events on

# Add a bit more scroll history in the buffer.
set -g history-limit 50000

# Enable color support inside of tmux.
set -g default-terminal "screen-256color"

# Ensure window titles get renamed automatically.
setw -g automatic-rename

# Ensure window index numbers get reordered on delete.
set-option -g renumber-windows on

# Start windows and panes index at 1, not 0.
set -g base-index 1
setw -g pane-base-index 1

# Enable full mouse support.
set -g mouse on

# Status bar optimized for Gruvbox.
set -g status-fg colour244
set -g status-bg default
set -g status-left ''
set -g status-right-length 0
#set -g status-right-length 20
#set -g status-right '%a %Y-%m-%d %H:%M'

set -g pane-border-fg default
set -g pane-border-bg default
set -g pane-active-border-fg colour250
set -g pane-active-border-bg default

set-window-option -g window-status-current-attr bold
set-window-option -g window-status-current-fg colour223

# -----------------------------------------------------------------------------
# Key bindings
# -----------------------------------------------------------------------------

# Unbind default keys
unbind C-b
unbind '"'
unbind %

# Reload the tmux config.
bind-key r source-file ~/.tmux.conf

# Split panes.
bind-key h split-window -v
bind-key v split-window -h

# Move around panes with ALT + arrow keys.
bind-key -n M-Up select-pane -U
bind-key -n M-Left select-pane -L
bind-key -n M-Down select-pane -D
bind-key -n M-Right select-pane -R

# -----------------------------------------------------------------------------
# Plugin Manager - https://github.com/tmux-plugins/tpm
# In order to use the plugins below you need to install TPM and the plugins.
#   Step 1) git clone https://github.com/tmux-plugins/tpm ~/.tmux/plugins/tpm
#   Step 2) Reload tmux if it's already started with `r
#   Step 3) Launch tmux and hit `I (capital i) to fetch any plugins
# -----------------------------------------------------------------------------

#bind -T copy-mode-vi y send-keys -X copy-pipe-and-cancel 'xclip -in -selection clipboard'
#`bind -t vi-copy y copy-pipe "xclip -sel clip -i"

# List of plugins.
set -g @plugin 'tmux-plugins/tpm'
set -g @plugin 'tmux-plugins/tmux-resurrect'
set -g @plugin 'tmux-plugins/tmux-yank'

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