I ran the AIO upgrade to v28 which failed.
All services now running but the server is in maint mode.
I cannot work out how to execute the occ command to turn it off.
I tried this:
docker exec -u www-data -it nextcloud-aio-nextcloud /bin/bash php /var/www/html/occ maintenance:mode --off
which results in this:
/usr/local/bin/php: cannot execute binary file