I had recently found the “Subscribe to Category” plugin, and Wordfence pointed out a vulnerability, so was looking for an alternative. I found Replyable, just tried to install, and got this fatal=error message:
Warning: require(/homepages/18/d221467449/htdocs/clickandbuilds/LackawannaCoalition/wp-content/plugins/postmatic/vendor/composer/../myclabs/deep-copy/src/DeepCopy/deep_copy.php): failed to open stream: No such file or directory in /homepages/18/d221467449/htdocs/clickandbuilds/LackawannaCoalition/wp-content/plugins/postmatic/vendor/composer/autoload_real.php on line 70
Fatal error: require(): Failed opening required '/homepages/18/d221467449/htdocs/clickandbuilds/LackawannaCoalition/wp-content/plugins/postmatic/vendor/composer/../myclabs/deep-copy/src/DeepCopy/deep_copy.php' (include_path='/homepages/18/d221467449/htdocs/clickandbuilds/LackawannaCoalition/wp-content/plugins/postmatic/vendor/phing/phing/classes:.:/usr/lib/php7.4') in /homepages/18/d221467449/htdocs/clickandbuilds/LackawannaCoalition/wp-content/plugins/postmatic/vendor/composer/autoload_real.php on line 70
I am a real amateur, so I am just going to remove the plug-in and keep looking, I am posting this here in case it helps someone else. My host is IONOS, if it matters.