The BackupWall plugin is missing, blank or fails in WHM, cPanel or DirectAdmin

cPanel: the BackupWall tile is missing for a user

Open WHM → Feature Manager and check that the feature backupwall is on for that user's feature list. The installer registers it as available by default.
The user plugin works in the Jupiter theme only. There is no Paper Lantern version.
Make sure both installers ran, in order: bash cpanel-plugin/whm/install.sh then bash cpanel-plugin/cpanel/install.sh. The cPanel one stops with a message if the WHM one has not been run.

The WHM plugin is limited to root-level WHM users; WHM resellers cannot open it.
Check cPanel is v100 or newer: the installer refuses older versions.
Run bash cpanel-plugin/whm/install.sh again.

Run bash directadmin-plugin/install.sh. It restarts DirectAdmin. If your admin account is not called admin, run DA_ADMIN=youradmin bash directadmin-plugin/install.sh.
Only the Evolution skin was checked.
There is no reseller level, only admin and user.

Check the BackupWall services are running: systemctl list-units 'backupwall*'. The plugins reach BackupWall on 127.0.0.1:8087; if it is down, they show nothing useful. See The console will not open or a service is down.
After an upgrade or an update, reload the panel page once; the plugin bundles are rebuilt in some builds. An update from Settings → Software updates does not change the plugins, so run the plugin installers again (the ones you use).
If you deleted the plugin's API key under Settings → API keys, run the plugin installer again to create a new one.
The plugin service key lives at /var/cpanel/backupwall/service.key (WHM and cPanel) or /usr/local/directadmin/plugins/backupwall/service.key (DirectAdmin). Do not copy or share it.

BackupWall talks to DirectAdmin with a stored login key named backupwall. If someone revokes it, backups fail until you run install.sh again.

Downloads resume only when the /backupwall-download web-server proxy is in place. On cPanel the installer sets it up for EA4 Apache only; LiteSpeed-only or nginx-only cPanel servers were not tested. On DirectAdmin a timer re-applies the proxy every 5 minutes, so after you switch DirectAdmin's web server, downloads can fail for up to 5 minutes.
A download link works until its 6-hour token expires, the file's 48-hour limit passes, it is deleted, an administrator uses "revoke all links", or the admin password changes.

There is no Plesk plugin. Use the console at https://<server-ip>:8087.