Cutom log in nextcloud.log

Hello dear all,

I wrote this script set with possibility forward some output to the nextcloud.log so that it looks like this:
image
Currently I have an idea to added some more information in log, like info about exactly files being touched by this preview generation process. But somehow I meet a problems with JSON format of logs.
Current output that does work is and simple (also as screenshot above):

{"app":"/var/www/nextcloud/occ preview:pre-generate","message":"+++ Cron Preview generation Completed. Execution time: 0 minutes and 12 seconds +++","level":1,"time":"2019-12-10T16:00:13+01:00","id":"5defb4ea487a3"}

What I would like to achieve is similar to this only that is File information per line not trace:
image
This is what does not work:

{"app":"/var/www/nextcloud/occ preview:pre-generate","level":1,"time":"2019-12-10T16:26:44+01:00","message":{"Message":"+++ Cron Preview generation Completed. Execution time: 0 minutes and 6 seconds +++","Trace":[{"user":"work","file":"[\/Shared\/Старое с Флэхи\/_Master_WPRG\/selfhtml\/perl\/sprache\/httpd.txt]"},{"user":"work","file":"[\/Shared\/Старое с Флэхи\/_Master_WPRG\/selfhtml\/perl\/sprache\/text.txt]"},{"user":"work","file":"[\/Shared\/Старое с Флэхи\/_Master_WPRG\/selfhtml\/src\/auge.gif]"},{"user":"work","file":"[\/Shared\/Старое с Флэхи\/_Master_WPRG\/selfhtml\/src\/css10.gif]"},{"user":"work","file":"[\/Shared\/Старое с Флэхи\/_Master_WPRG\/selfhtml\/src\/css20.gif]"},{"user":"work","file":"[\/Shared\/Старое с Флэхи\/_Master_WPRG\/selfhtml\/servercgi\/cgi\/formular.gif]"}]}}

The same a bit formatted to read:

{"app":"/var/www/nextcloud/occ preview:pre-generate","level":1,"time":"2019-12-10T16:26:44+01:00","message":
{"Message":"+++ Cron Preview generation Completed. Execution time: 0 minutes and 6 seconds +++","Trace":[
{"user":"work","file":"[\/Shared\/Старое с Флэхи\/_Master_WPRG\/selfhtml\/perl\/sprache\/httpd.txt]"},
{"user":"work","file":"[\/Shared\/Старое с Флэхи\/_Master_WPRG\/selfhtml\/perl\/sprache\/text.txt]"},
{"user":"work","file":"[\/Shared\/Старое с Флэхи\/_Master_WPRG\/selfhtml\/src\/auge.gif]"},
{"user":"work","file":"[\/Shared\/Старое с Флэхи\/_Master_WPRG\/selfhtml\/src\/css10.gif]"},
{"user":"work","file":"[\/Shared\/Старое с Флэхи\/_Master_WPRG\/selfhtml\/src\/css20.gif]"},
{"user":"work","file":"[\/Shared\/Старое с Флэхи\/_Master_WPRG\/selfhtml\/servercgi\/cgi\/formular.gif]"}]}}

How should it be formatted to show file info per line?