Only see 3 textarea field on Plugin Setting Page
After shuffle all textareaField, I found the 4th one custApptReminder1 misspell in function defineSettings() at my plugin.php. After corrected it, the field is show up.

protected function defineSettings()
    {
        return array(
            'custAccountCreation' =&gt; array(AttributeType::String),
            'custAccountCreationSubject' =&gt; array(AttributeType::String),
            'custApptReminder'=&gt; array(AttributeType::String),
            'custApptReminder1'=&gt; array(AttributeType::String),
        );
    }