SSHFS - Can't login using IdentityFile

I'm using this command to connect from LEDE router to OpenWRT Chaos Calmer router and mount those folders but I it keeps asking me for password.

sshfs -o allow_other,IdentityFile=/root/.ssh/id_rsa_ubnt-erx_sshfs root@ /mnt/erx01

What am I doing wrong?

I know this one is really old, but I have the very same issue in my X86-64 installation running 19.07.4.

What I want to achive: ACME running on router vm that shall distribute wildcard-certificate to several vms after each renewal.
Router: a.k.a
Ubuntu vm:
Ubuntu folder I need access to: /etc/ssl/private/folder
openwrt folder for mounting: /etc/ssl/private-
key file /etc/ssh/id_rsa
content of /etc/ssh/ has been inserted into Ubuntu's authorized_keys file
Ubuntu's ssh daemon is listening to port 100

So by following each single tutorial in the web the instruction should be:

root@Router:~# sshfs -o IdentityFile=/etc/ssh/id_rsa -p 100 root@ /etc/ssl/private-
fuse: failed to open mountpoint for reading: Permission denied

Can someone help? Connecting as root via winscp (after converting private key from openssh format to putty format) works from client device

edit: This seems to have been a leftover problem of former nfs tests I did. umount /etc/ssl/private- followed by a reboot solved the problem