https://www.mecabricks.com/en/credits

so you have to pay a certain amount to get renders?

No, you can do it for free but with limited features, as you can see on the credits page. You can only make 10 free renders during 24 hours(Daily limit) and they are only stored for 3 days on the server.

But remember that just because it say it's free, it's actually paid by Scrubs who have built the render farm setup that makes the magic(lots of expensive hardware). It's located in his house so he pays for the electric bill and internet connection to run the render services on Mecabricks. So if you can, don't only make free renders, if you can, please support Scrubs so he can continue to make these awesome tools even better! 😃