Automatic TM fill-up is part of the Growth plan according to this:
Setting Up Translation Memory Fill-up | Transifex Help Center
I’ve recently started as a maintainer for an open source project and we don’t pay for any special plan, but it seems like we have access to TM fill-up of 100% and 101% matches, plus TM fill-up across similar languages. Have you changed it so TM fill-up is a free feature now?