When I enabled the plugin, I got the following alarm.
Unexpected output of 4542 characters was generated during plugin activation. If you notice “headers already sent” messages, RSS feed issues, or other glitches, try stopping or removing this plugin.
I tried again on the rental server. This time there is no alarm when activated. However, I click ‘new message’, user page is displayed.
setting > General > Front End PM page > user → email page
I changed it to the email page, but it is not reflected.
The email page has a [front end pm] shortcode only.
Before enabling Ultimate member, the ‘new message’ template is displayed, but when Ultimate member is enabled, user page of Ultimate Member is displayed.
If you do not want to use UM page for this plugin, do not install Front End PM -Integration plugin.
Then set Front End PM > Settings > General > Front End PM Page to that page (which has the shortcode)