Seafile fails to install on Plesk

I have been trying to install Seafile on one domain on my Plesk VPN server, to act as a webDAV server, primarily for uploading files too large to add to e-mails as attachments (so that others can download them).
I have follwed the (meagre) instructions in Plesk, and reached the point of clicking ‘Install’.
The progress bar runs to about 50% and then stops with an error message telling me to look in the logs.
I have found many logs under ‘Seafile > Logs’ for the domain in question. These only appear AFTER the attempted installation, although some of the log files pre-date the installation attempt. It is not clear which logs may contain anything useful.
Safile.log contains the following lines (repeated every ten seconds for about two minutes:

2022-10-26 10:58:51 socket file exists, delete it anyway
2022-10-26 10:58:51 …/common/seaf-utils.c(333): Use database Mysql
2022-10-26 10:58:51 http-server.c(192): fileserver: worker_threads = 10
2022-10-26 10:58:51 http-server.c(207): fileserver: fixed_block_size = 8388608
2022-10-26 10:58:51 http-server.c(222): fileserver: web_token_expire_time = 3600
2022-10-26 10:58:51 http-server.c(237): fileserver: max_indexing_threads = 1
2022-10-26 10:58:51 http-server.c(252): fileserver: max_index_processing_threads= 3
2022-10-26 10:58:51 http-server.c(274): fileserver: cluster_shared_temp_file_mode = 600
2022-10-26 10:58:51 http-server.c(2794): Could not bind socket: Address already in use

Controller.log contains the following lines, again repeated evert ten seconds:

2022-10-26 11:41:23 seafile-controller.c(416): pid file /var/www/vhosts/ramasaig.com/seafile/pids/seaf-server.pid does not exist
2022-10-26 11:41:23 seafile-controller.c(437): seaf-server need restart…
2022-10-26 11:41:23 seafile-controller.c(190): starting seaf-server …
2022-10-26 11:41:23 seafile-controller.c(81): spawn_process: seaf-server -F
/var/www/vhosts/ramasaig.com/seafile/conf -c
/var/www/vhosts/ramasaig.com/seafile/ccnet -d
/var/www/vhosts/ramasaig.com/seafile/seafile-data -l /var/www/vhosts/ramasaig.com/seafile/logs/seafile.log -P
/var/www/vhosts/ramasaig.com/seafile/pids/seaf-server.pid -p
/var/www/vhosts/ramasaig.com/seafile/seafile-server-8.0.8/runtime
2022-10-26 11:41:23 seafile-controller.c(115): spawned seaf-server, pid 664096

Obviously there’s something wrong (Ports requiring setting?) and there’s a file missing. But it’s not clear what I should do about it. I am assuming that the Seafile package available in Plesk is complete and doesn’t require additional files. Can anyone offer some help, please.
Regards,
Tim Dawson