Mailgun - сost and rate plans for new users

I would like to set up an email newsletter. So far it’s no more than 50 emails per month.
I can’t understand the pricing policy of mailgun. I choose the flex on this page: Flexible Pricing & Email Delivery Plans - Email API Service | Mailgun and I get here: Sign Up Free | Mailgun And now I’m offered the foundation trial rate. If I choose this option, do I have to pay $15 a month after three months?

I don’t want to pay a fixed amount every month. I would like to pay only for emails sent. Is this still possible with mailgun?
Sorry for my English.

If you stay on the Flex plan, you’ll only pay for the emails you send. There is no monthly fee.

They’ve changed their pricing. The “Flex Plan” auto upgrades to a paid plan (Foundation). What you need to do is manually downgrade to the Flex Plan before your 3 month trial is up to avoid the monthly $35 fee.

Thank you, that’s what I wanted to know. You have helped me a lot.