Customizing REPL keybindings with alt keys

[haji-ali]

I am following the docs to customize my key bindings.
However, the following code in my startup.jl (taken from the docs)

import REPL
import REPL.LineEdit

const mykeys = Dict{Any,Any}(
    "\\Mt" => (s,o...)->(LineEdit.edit_delete_prev_word(s))
)

function customize_keys(repl)
    repl.interface = REPL.setup_interface(repl; extra_repl_keymap = mykeys)
end

atreplinit(customize_keys)

Gives the assertion

AssertionError: c == '-'

when I start julia and the key Alt+t does not work. Changing \\Mt to another key like ^t seems to work on the other hand.