First of all, you most likely need to use `chansend()` function. I don't have `term_sendkeys()` in my `neovim` instance, so it's probably from some plugin. Also, the `i` is unnecessary, since this function can't put you into insert mode.

Now, regarding your problem. `"\<Up>"` does indeed have some unexpected behavior inside double quotes. But, I managed to work around it like this:

1. Open `vim` preemptively to not get error on load.
2. While in terminal, start by writing `echo -n '' >> ~/.vimrc`, then put cursor between quotes and press `control-v` followed by `Up`, then `enter` to execute your command.
3. Reload `.vimrc` with `:e!`, delete the last line with literal `Up` sequence, and `p` it wherever you want (in this case, into `chansend` function).

This seem to work correctly:

    call chansend(b:terminal_job_id, '^[OA' . "\<cr>")

Do not try to copy code from here, though. You need to get actual literal `Up` sequence from your shell.