Issue Installing Openwrt on Ubiquiti 6 plus

[notheld]

I'm having trouble installing OpenWrt on my Ubiquiti 6 Plus. I'm following these instructions LINK

I downloaded this binary to perform the installation LINK

However, in step 6, I am unable to send the file to the U6+, and I am getting this error:

scp openwrt.bin ubnt@192.168.1.20:/tmp/
** WARNING: connection is not using a post-quantum key exchange algorithm.
** This session may be vulnerable to "store now, decrypt later" attacks.
** The server may need to be upgraded. See https://openssh.com/pq.html
ubnt@192.168.1.20's password:
ash: /usr/libexec/sftp-server: not found
scp: Connection closed

So I went to investigate the contents of this directory that appears in the error:

U6-Plus-BZ.6.5.28# ls -lha /usr/libexec/
drwxr-xr-x    2 ui       root          60 Aug 30  2018 .
drwxr-xr-x    8 ui       root         180 Aug 30  2018 ..
-rwxrwxr-x    1 ui       root         105 Jan 27  2023 login.sh

So there is only this script, and this is its content:

U6-Plus-BZ.6.5.28# cat  /usr/libexec/login.sh
#!/bin/sh

[ "$(uci -q get system.@system[0].ttylogin)" == 1 ] || exec /bin/ash --login

exec /bin/login

The only open TCP port is 22:

U6-Plus-BZ.6.5.28# netstat -nlutp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      3109/dropbear
tcp        0      0 :::22                   :::*                    LISTEN      3109/dropbear
udp        0      0 0.0.0.0:10001           0.0.0.0:*                           13463/mcad
udp        0      0 0.0.0.0:34649           0.0.0.0:*                           13463/mcad
udp        0      0 0.0.0.0:39546           0.0.0.0:*                           2650/ntpd
udp        0      0 :::51499                :::*                                13463/mcad

Does anyone have any insight into this problem?

If it is no longer possible to send using scp, what other alternative can I use to send the binary file? From what I understand, this device does not have a web interface to access. I simply took it out of the box and started the procedure by just connecting the device to PoE; I am not using a switch.

Is my only alternative to downgrade the system version of this device?

[psherman]

@notheld

scp openwrt.bin ubnt@192.168.1.20:/tmp/

try adding the -O argument (that is the capital letter O, not the number zero):

scp -O openwrt.bin ubnt@192.168.1.20:/tmp/

[notheld]

Thank you very much, psherman.

Your suggestion worked perfectly.

For those who are curious, this is the description of the -O parameter:

       -O      Use the legacy SCP protocol for file transfers instead of
               the SFTP protocol.  Forcing the use of the SCP protocol
               may be necessary for servers that do not implement SFTP,
               for backwards-compatibility for particular filename
               wildcard patterns and for expanding paths with a ‘~’
               prefix for older SFTP servers.