Trying to update plugin - "Plugin is not valid, it is missing the plugin.json file."

Support & Bugs
1

Hello! I’m trying to update the MarketingCampaignsReporting-plugin. I get 2 messages:

“Plugin is not valid, it is missing the plugin.json file.”

WARNING: /plugins/CorePluginsAdmin/PluginInstaller.php(261): Warning - opendir(/usr/www/users/myuser/public_html/matomo-user/tmp/latest/plugins/bd9032234b0af64c040bc660c8919e18/): Failed to open directory: No such file or directory - Matomo 5.2.2 - Please report this message in the Matomo forums: https://forum.matomo.org (please do a search first as it might have been reported already) (Module: Marketplace, Action: updatePlugin, In CLI mode: false)

Any ideas what the problem might be?

Additional information:
The file /usr/www/users/myuser/public_html/matomo/plugins/MarketingCampaignsReporting/plugin.json
does exist.

I use
define(‘PIWIK_USER_PATH’, $_SERVER[‘DOCUMENT_ROOT’].‘/matomo-user/’);
in bootstrap.php to set the USER_PATH.