Update settings.php

apps/user_webdavauth/templates/settings.php

 <form id="webdavauth" action="#" method="post">
 	<fieldset class="personalblock">
 		<legend><strong><?php p($l->t('WebDAV Authentication'));?></strong></legend>
-		<p><label for="webdav_url"><?php p($l->t('URL: '));?><input type="url" placeholder=<?php p($l->t('https://example.com/webdav'));?> id="webdav_url" name="webdav_url" value="<?php p($_['webdav_url']); ?>"></label>
+		<p><label for="webdav_url"><?php p($l->t('URL: '));?><input type="url" placeholder="https://example.com/webdav" id="webdav_url" name="webdav_url" value="<?php p($_['webdav_url']); ?>"></label>
 		 <input type="hidden" name="requesttoken" value="<?php p($_['requesttoken']) ?>" id="requesttoken">
 		<input type="submit" value="Save" />
 		<br /><?php p($l->t('ownCloud will send the user credentials to this URL. This plugin checks the response and will interpret the HTTP statuscodes 401 and 403 as invalid credentials, and all other responses as valid credentials.')); ?>