Clicking the renewal link in the 'expired' email...
../index.php?option=com_payplans&view=subscription&task=display&subscription_key=8O56WJCMAUG6
produces...
404 - View not found [name, type, prefix]: subscription, html, payplansView
Edit:
Joomla 3.9.3
PHP 7.2.6
Have tried clicking link while logged in and logged out. No change.
Update: Attempted re-install. Failed.