You should receive an invoice as well as email #4 (the first paid lesson) momentarily.
A few other helpful tips:
1. If you did not sign up for the free trial then you can access email lessons #1-#3 from the bottom section of email #4.
2. If you ever encounter any technical issues, such as you didn't receive an email, please email me at email@example.com.
3. Additionally, monthly subscribers can cancel their subscription (i.e. any remaining billing cycles) at any time by emailing your request to firstname.lastname@example.org.
That's really it. I hope you enjoy the full series!