app/views/payment_mailer/payment_notification_email.html.erb
<!DOCTYPE html>
<html>
<head>
<meta content='text/html; charset=UTF-8' http-equiv='Content-Type' />
</head>
<body>
<h1><%= @user.name || @user.email %>,</h1>
<p><%= @payee.name || @payee.email %> has requested a payment on RMMTS.</p>
<p>If you think this is in error, talk to them about it.</p>
</body>
</html>